wrangle.knit

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# .black.big-text[Data<br>Wrangling]
## .black[Session - 4]

---

# Course Progress

---

# What is Data wrangling?

- "data exploration and data manipulation" [(Jesse Mostipak)](https://www.kaggle.com/jessemostipak/dive-into-dplyr-tutorial-1)

- "tidying and transforming" [(Hadley & Garrett)](https://r4ds.had.co.nz/index.html)

---

# "Transforming" data means:

- "narrowing in on observations of interest ...

- creating new variables that are functions of existing variables ... and

- calculating a set of summary statistics."

---

class: hide-count, middle, hide-logo
background-image: url(images/dplyr.svg)
background-size: contain
background-position: right

# .big-text[R<br>Package]

---

# `dplyr` package

- "dplyr is a grammar of data manipulation"

- "providing a consistent set of verbs that help you solve the most common data manipulation challenges:"

- Few important functions:
  - `filter()` 
  - `select()` 
  - `mutate()` 
  - `arrange()` 
  - `summarise()`

---

# `filter()` function:

- Picks cases based on their values.

---

# How to have a data of only Gentoo penguins?

---

```r
# there are three species: Chinstrap, Gentoo, Adelie
penguins %>% 
* filter(species == "Gentoo")
```
]

```
## # A tibble: 124 × 8
##    species island bill_length_mm bill_depth_mm flipper_len…¹ body_…² sex    year
##    <fct>   <fct>           <dbl>         <dbl>         <int>   <int> <fct> <int>
##  1 Gentoo  Biscoe           46.1          13.2           211    4500 fema…  2007
##  2 Gentoo  Biscoe           50            16.3           230    5700 male   2007
##  3 Gentoo  Biscoe           48.7          14.1           210    4450 fema…  2007
##  4 Gentoo  Biscoe           50            15.2           218    5700 male   2007
##  5 Gentoo  Biscoe           47.6          14.5           215    5400 male   2007
##  6 Gentoo  Biscoe           46.5          13.5           210    4550 fema…  2007
##  7 Gentoo  Biscoe           45.4          14.6           211    4800 fema…  2007
##  8 Gentoo  Biscoe           46.7          15.3           219    5200 male   2007
##  9 Gentoo  Biscoe           43.3          13.4           209    4400 fema…  2007
## 10 Gentoo  Biscoe           46.8          15.4           215    5150 male   2007
## # … with 114 more rows, and abbreviated variable names ¹flipper_length_mm,
## #   ²body_mass_g
```

]
]

---

```r
# there are three species: Chinstrap, Gentoo, Adelie

praw <- read_csv("data/gentoo-penguins1.csv")

praw %>% 
  filter(species == "Gentoo") %>% 
  summary() %>% 
  kableExtra::kable()
```
]

<table>
 <thead>
  <tr>
   <th style="text-align:left;">   </th>
   <th style="text-align:left;">   species </th>
   <th style="text-align:left;">    island </th>
   <th style="text-align:left;"> bill_length_mm </th>
   <th style="text-align:left;"> bill_depth_mm </th>
   <th style="text-align:left;"> flipper_length_mm </th>
   <th style="text-align:left;">  body_mass_g </th>
   <th style="text-align:left;">     sex </th>
   <th style="text-align:left;">      year </th>
  </tr>
 </thead>
<tbody>
  <tr>
   <td style="text-align:left;">  </td>
   <td style="text-align:left;"> Length:124 </td>
   <td style="text-align:left;"> Length:124 </td>
   <td style="text-align:left;"> Min.   :40.90 </td>
   <td style="text-align:left;"> Min.   :13.10 </td>
   <td style="text-align:left;"> Min.   :203.0 </td>
   <td style="text-align:left;"> Min.   :3950 </td>
   <td style="text-align:left;"> Length:124 </td>
   <td style="text-align:left;"> Min.   :2007 </td>
  </tr>
  <tr>
   <td style="text-align:left;">  </td>
   <td style="text-align:left;"> Class :character </td>
   <td style="text-align:left;"> Class :character </td>
   <td style="text-align:left;"> 1st Qu.:45.30 </td>
   <td style="text-align:left;"> 1st Qu.:14.20 </td>
   <td style="text-align:left;"> 1st Qu.:212.0 </td>
   <td style="text-align:left;"> 1st Qu.:4500 </td>
   <td style="text-align:left;"> Class :character </td>
   <td style="text-align:left;"> 1st Qu.:2007 </td>
  </tr>
  <tr>
   <td style="text-align:left;">  </td>
   <td style="text-align:left;"> Mode  :character </td>
   <td style="text-align:left;"> Mode  :character </td>
   <td style="text-align:left;"> Median :47.30 </td>
   <td style="text-align:left;"> Median :15.00 </td>
   <td style="text-align:left;"> Median :216.0 </td>
   <td style="text-align:left;"> Median :4925 </td>
   <td style="text-align:left;"> Mode  :character </td>
   <td style="text-align:left;"> Median :2008 </td>
  </tr>
  <tr>
   <td style="text-align:left;">  </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> Mean   :47.50 </td>
   <td style="text-align:left;"> Mean   :14.98 </td>
   <td style="text-align:left;"> Mean   :217.2 </td>
   <td style="text-align:left;"> Mean   :4985 </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> Mean   :2008 </td>
  </tr>
  <tr>
   <td style="text-align:left;">  </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> 3rd Qu.:49.55 </td>
   <td style="text-align:left;"> 3rd Qu.:15.70 </td>
   <td style="text-align:left;"> 3rd Qu.:221.0 </td>
   <td style="text-align:left;"> 3rd Qu.:5400 </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> 3rd Qu.:2009 </td>
  </tr>
  <tr>
   <td style="text-align:left;">  </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> Max.   :59.60 </td>
   <td style="text-align:left;"> Max.   :17.30 </td>
   <td style="text-align:left;"> Max.   :231.0 </td>
   <td style="text-align:left;"> Max.   :6050 </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> Max.   :2009 </td>
  </tr>
  <tr>
   <td style="text-align:left;">  </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> NA's   :1 </td>
   <td style="text-align:left;"> NA's   :1 </td>
   <td style="text-align:left;"> NA's   :1 </td>
   <td style="text-align:left;"> NA's   :1 </td>
   <td style="text-align:left;"> NA </td>
   <td style="text-align:left;"> NA </td>
  </tr>
</tbody>
</table>

]
]

---

# How to export data file to your computer?

---

```r
# three species are Chinstrap, Gentoo, Adelie
penguins %>% 
  filter(species == "Gentoo") %>% 
* write_csv("data/gentoo-penguins.csv")

```
]

]
]

---

# ✋ WAIT! What is `%>% `

- this is called **pipe** ( `%>%` = control + shift + m)

- "a powerful tool for clearly expressing a sequence of **multiple operations**"

- interpret/read it as **then**.

```r
penguins %>% 
  filter(species == "Gentoo") %>% 
  summary() %>% 
  kableExtra::kable()
```

---

# Comparison: Relational Operators

`x < y`

`x > y`

`x <= y`

`x >= y`

`x == y` (equal)

`x != y` (not equal)

---
class: center, middle

# How to have a data of penguins with bill length more than 43 mm?

---

```r
penguins %>% 
  filter(bill_length_mm > 43) 
```
]

```
## # A tibble: 188 × 8
##    species island    bill_length_mm bill_depth_mm flipper_…¹ body_…² sex    year
##    <fct>   <fct>              <dbl>         <dbl>      <int>   <int> <fct> <int>
##  1 Adelie  Torgersen           46            21.5        194    4200 male   2007
##  2 Adelie  Dream               44.1          19.7        196    4400 male   2007
##  3 Adelie  Torgersen           45.8          18.9        197    4150 male   2008
##  4 Adelie  Dream               43.2          18.5        192    4100 male   2008
##  5 Adelie  Biscoe              43.2          19          197    4775 male   2009
##  6 Adelie  Biscoe              45.6          20.3        191    4600 male   2009
##  7 Adelie  Torgersen           44.1          18          210    4000 male   2009
##  8 Adelie  Torgersen           43.1          19.2        197    3500 male   2009
##  9 Gentoo  Biscoe              46.1          13.2        211    4500 fema…  2007
## 10 Gentoo  Biscoe              50            16.3        230    5700 male   2007
## # … with 178 more rows, and abbreviated variable names ¹flipper_length_mm,
## #   ²body_mass_g
```

]
]

---
class: center, middle

# How to have a data of Gentoo penguins with bill length more than 55 mm?

---
.panelset[

```r
penguins %>% 
  filter(species == "Gentoo",
         bill_length_mm > 55)
```
]

```
## # A tibble: 3 × 8
##   species island bill_length_mm bill_depth_mm flipper_leng…¹ body_…² sex    year
##   <fct>   <fct>           <dbl>         <dbl>          <int>   <int> <fct> <int>
## 1 Gentoo  Biscoe           59.6            17            230    6050 male   2007
## 2 Gentoo  Biscoe           55.9            17            228    5600 male   2009
## 3 Gentoo  Biscoe           55.1            16            230    5850 male   2009
## # … with abbreviated variable names ¹flipper_length_mm, ²body_mass_g
```

]
]

---
class: center, middle

# How to have data of non-Gentoo penguins with bill length more than 45 mm and weight more than 4 kg?

---

```r
penguins %>% 
  filter(species != "Gentoo",
         bill_length_mm > 45,
         body_mass_g > 4000)
```
]

```
## # A tibble: 18 × 8
##    species   island    bill_length_mm bill_depth_mm flippe…¹ body_…² sex    year
##    <fct>     <fct>              <dbl>         <dbl>    <int>   <int> <fct> <int>
##  1 Adelie    Torgersen           46            21.5      194    4200 male   2007
##  2 Adelie    Torgersen           45.8          18.9      197    4150 male   2008
##  3 Adelie    Biscoe              45.6          20.3      191    4600 male   2009
##  4 Chinstrap Dream               46            18.9      195    4150 fema…  2007
##  5 Chinstrap Dream               52            18.1      201    4050 male   2007
##  6 Chinstrap Dream               50.5          19.6      201    4050 male   2007
##  7 Chinstrap Dream               49.2          18.2      195    4400 male   2007
##  8 Chinstrap Dream               52            19        197    4150 male   2007
##  9 Chinstrap Dream               52.8          20        205    4550 male   2008
## 10 Chinstrap Dream               54.2          20.8      201    4300 male   2008
## 11 Chinstrap Dream               51            18.8      203    4100 male   2008
## 12 Chinstrap Dream               52            20.7      210    4800 male   2008
## 13 Chinstrap Dream               53.5          19.9      205    4500 male   2008
## 14 Chinstrap Dream               50.8          18.5      201    4450 male   2009
## 15 Chinstrap Dream               49            19.6      212    4300 male   2009
## 16 Chinstrap Dream               50.7          19.7      203    4050 male   2009
## 17 Chinstrap Dream               49.3          19.9      203    4050 male   2009
## 18 Chinstrap Dream               50.8          19        210    4100 male   2009
## # … with abbreviated variable names ¹flipper_length_mm, ²body_mass_g
```

]
]

---
class: center, middle

# How to have only top or bottom rows from data?

---

```r
penguins %>% 
  filter(species != "Gentoo",
         bill_length_mm > 45,
         body_mass_g > 4000) %>% 
* head()
```
]

```
## # A tibble: 6 × 8
##   species   island    bill_length_mm bill_depth_mm flipper…¹ body_…² sex    year
##   <fct>     <fct>              <dbl>         <dbl>     <int>   <int> <fct> <int>
## 1 Adelie    Torgersen           46            21.5       194    4200 male   2007
## 2 Adelie    Torgersen           45.8          18.9       197    4150 male   2008
## 3 Adelie    Biscoe              45.6          20.3       191    4600 male   2009
## 4 Chinstrap Dream               46            18.9       195    4150 fema…  2007
## 5 Chinstrap Dream               52            18.1       201    4050 male   2007
## 6 Chinstrap Dream               50.5          19.6       201    4050 male   2007
## # … with abbreviated variable names ¹flipper_length_mm, ²body_mass_g
```

]
]

---

```r
penguins %>% 
  filter(species != "Gentoo",
         bill_length_mm > 45,
         body_mass_g > 4000) %>% 
* tail(3)
```
]

```
## # A tibble: 3 × 8
##   species   island bill_length_mm bill_depth_mm flipper_le…¹ body_…² sex    year
##   <fct>     <fct>           <dbl>         <dbl>        <int>   <int> <fct> <int>
## 1 Chinstrap Dream            50.7          19.7          203    4050 male   2009
## 2 Chinstrap Dream            49.3          19.9          203    4050 male   2009
## 3 Chinstrap Dream            50.8          19            210    4100 male   2009
## # … with abbreviated variable names ¹flipper_length_mm, ²body_mass_g
```

]
]

---

# 🧠 YOUR TURN

How many Chinstrap penguins are with bill length more than 45 mm and weight more than 4 kg?
]

```r
penguins %>% 
  filter(species == "Chinstrap",
         bill_length_mm > 45,
         body_mass_g > 4000) %>% 
  head()
```

]

```
## # A tibble: 6 × 8
##   species   island bill_length_mm bill_depth_mm flipper_le…¹ body_…² sex    year
##   <fct>     <fct>           <dbl>         <dbl>        <int>   <int> <fct> <int>
## 1 Chinstrap Dream            46            18.9          195    4150 fema…  2007
## 2 Chinstrap Dream            52            18.1          201    4050 male   2007
## 3 Chinstrap Dream            50.5          19.6          201    4050 male   2007
## 4 Chinstrap Dream            49.2          18.2          195    4400 male   2007
## 5 Chinstrap Dream            52            19            197    4150 male   2007
## 6 Chinstrap Dream            52.8          20            205    4550 male   2008
## # … with abbreviated variable names ¹flipper_length_mm, ²body_mass_g
```

]
]

---

# `select()` function: Chooses rows based on column values.

---
class: center, middle

# How to have only `species` variable in data?

---

```r
penguins %>% 
* select(species)
```
]

```
## # A tibble: 344 × 1
##    species
##    <fct>  
##  1 Adelie 
##  2 Adelie 
##  3 Adelie 
##  4 Adelie 
##  5 Adelie 
##  6 Adelie 
##  7 Adelie 
##  8 Adelie 
##  9 Adelie 
## 10 Adelie 
## # … with 334 more rows
```

]
]

---
class: center, middle

# How to have a specific range of variables in data?

---

```r
penguins %>% 
  select(species : bill_depth_mm)
```
]

```
## # A tibble: 344 × 4
##    species island    bill_length_mm bill_depth_mm
##    <fct>   <fct>              <dbl>         <dbl>
##  1 Adelie  Torgersen           39.1          18.7
##  2 Adelie  Torgersen           39.5          17.4
##  3 Adelie  Torgersen           40.3          18  
##  4 Adelie  Torgersen           NA            NA  
##  5 Adelie  Torgersen           36.7          19.3
##  6 Adelie  Torgersen           39.3          20.6
##  7 Adelie  Torgersen           38.9          17.8
##  8 Adelie  Torgersen           39.2          19.6
##  9 Adelie  Torgersen           34.1          18.1
## 10 Adelie  Torgersen           42            20.2
## # … with 334 more rows
```

]
]

---
class: center, middle

# How to have variables based upon their location in data?

---

```r
penguins %>% 
  select(4:8)
```
]

```
## # A tibble: 344 × 5
##    bill_depth_mm flipper_length_mm body_mass_g sex     year
##            <dbl>             <int>       <int> <fct>  <int>
##  1          18.7               181        3750 male    2007
##  2          17.4               186        3800 female  2007
##  3          18                 195        3250 female  2007
##  4          NA                  NA          NA <NA>    2007
##  5          19.3               193        3450 female  2007
##  6          20.6               190        3650 male    2007
##  7          17.8               181        3625 female  2007
##  8          19.6               195        4675 male    2007
##  9          18.1               193        3475 <NA>    2007
## 10          20.2               190        4250 <NA>    2007
## # … with 334 more rows
```

]
]

---
class: center, middle

# How to have specific variables in data?

---

```r
penguins %>% 
  select(species, body_mass_g, year)
```
]

```
## # A tibble: 344 × 3
##    species body_mass_g  year
##    <fct>         <int> <int>
##  1 Adelie         3750  2007
##  2 Adelie         3800  2007
##  3 Adelie         3250  2007
##  4 Adelie           NA  2007
##  5 Adelie         3450  2007
##  6 Adelie         3650  2007
##  7 Adelie         3625  2007
##  8 Adelie         4675  2007
##  9 Adelie         3475  2007
## 10 Adelie         4250  2007
## # … with 334 more rows
```

]
]

---

```r
penguins %>% 
  select(-c(species, body_mass_g, year))
```
]

```
## # A tibble: 344 × 5
##    island    bill_length_mm bill_depth_mm flipper_length_mm sex   
##    <fct>              <dbl>         <dbl>             <int> <fct> 
##  1 Torgersen           39.1          18.7               181 male  
##  2 Torgersen           39.5          17.4               186 female
##  3 Torgersen           40.3          18                 195 female
##  4 Torgersen           NA            NA                  NA <NA>  
##  5 Torgersen           36.7          19.3               193 female
##  6 Torgersen           39.3          20.6               190 male  
##  7 Torgersen           38.9          17.8               181 female
##  8 Torgersen           39.2          19.6               195 male  
##  9 Torgersen           34.1          18.1               193 <NA>  
## 10 Torgersen           42            20.2               190 <NA>  
## # … with 334 more rows
```

]
]

---

# `mutate()` function: Adds new variables that are functions of existing variables

---

# How to convert penguin body mass from grams to kilograms?

---

```r
penguins %>% 
* mutate(body_mass_kg = body_mass_g / 1000)
```
]

```
## # A tibble: 344 × 9
##    species island    bill_length_mm bill_d…¹ flipp…² body_…³ sex    year body_…⁴
##    <fct>   <fct>              <dbl>    <dbl>   <int>   <int> <fct> <int>   <dbl>
##  1 Adelie  Torgersen           39.1     18.7     181    3750 male   2007    3.75
##  2 Adelie  Torgersen           39.5     17.4     186    3800 fema…  2007    3.8 
##  3 Adelie  Torgersen           40.3     18       195    3250 fema…  2007    3.25
##  4 Adelie  Torgersen           NA       NA        NA      NA <NA>   2007   NA   
##  5 Adelie  Torgersen           36.7     19.3     193    3450 fema…  2007    3.45
##  6 Adelie  Torgersen           39.3     20.6     190    3650 male   2007    3.65
##  7 Adelie  Torgersen           38.9     17.8     181    3625 fema…  2007    3.62
##  8 Adelie  Torgersen           39.2     19.6     195    4675 male   2007    4.68
##  9 Adelie  Torgersen           34.1     18.1     193    3475 <NA>   2007    3.48
## 10 Adelie  Torgersen           42       20.2     190    4250 <NA>   2007    4.25
## # … with 334 more rows, and abbreviated variable names ¹bill_depth_mm,
## #   ²flipper_length_mm, ³body_mass_g, ⁴body_mass_kg
```

]
]

---

```r
penguins %>% 
  select(body_mass_g) %>%
  mutate(body_mass_kg = body_mass_g / 1000)
```
]

```
## # A tibble: 344 × 2
##    body_mass_g body_mass_kg
##          <int>        <dbl>
##  1        3750         3.75
##  2        3800         3.8 
##  3        3250         3.25
##  4          NA        NA   
##  5        3450         3.45
##  6        3650         3.65
##  7        3625         3.62
##  8        4675         4.68
##  9        3475         3.48
## 10        4250         4.25
## # … with 334 more rows
```

]
]

---

```r
penguins %>% 
  mutate(body_mass_kg = body_mass_g / 1000, 
         bill = bill_length_mm * bill_depth_mm)
```
]

```
## # A tibble: 344 × 10
##    species island    bill_le…¹ bill_…² flipp…³ body_…⁴ sex    year body_…⁵  bill
##    <fct>   <fct>         <dbl>   <dbl>   <int>   <int> <fct> <int>   <dbl> <dbl>
##  1 Adelie  Torgersen      39.1    18.7     181    3750 male   2007    3.75  731.
##  2 Adelie  Torgersen      39.5    17.4     186    3800 fema…  2007    3.8   687.
##  3 Adelie  Torgersen      40.3    18       195    3250 fema…  2007    3.25  725.
##  4 Adelie  Torgersen      NA      NA        NA      NA <NA>   2007   NA      NA 
##  5 Adelie  Torgersen      36.7    19.3     193    3450 fema…  2007    3.45  708.
##  6 Adelie  Torgersen      39.3    20.6     190    3650 male   2007    3.65  810.
##  7 Adelie  Torgersen      38.9    17.8     181    3625 fema…  2007    3.62  692.
##  8 Adelie  Torgersen      39.2    19.6     195    4675 male   2007    4.68  768.
##  9 Adelie  Torgersen      34.1    18.1     193    3475 <NA>   2007    3.48  617.
## 10 Adelie  Torgersen      42      20.2     190    4250 <NA>   2007    4.25  848.
## # … with 334 more rows, and abbreviated variable names ¹bill_length_mm,
## #   ²bill_depth_mm, ³flipper_length_mm, ⁴body_mass_g, ⁵body_mass_kg
```

]
]

---

```r
penguins %>% 
  mutate(body_mass_kg = body_mass_g / 1000,
         bill = bill_length_mm * bill_depth_mm) %>% 
  select(body_mass_kg,
         bill)
```
]

```
## # A tibble: 344 × 2
##    body_mass_kg  bill
##           <dbl> <dbl>
##  1         3.75  731.
##  2         3.8   687.
##  3         3.25  725.
##  4        NA      NA 
##  5         3.45  708.
##  6         3.65  810.
##  7         3.62  692.
##  8         4.68  768.
##  9         3.48  617.
## 10         4.25  848.
## # … with 334 more rows
```

]
]

---

# `arrange()` function: Changes the order of the rows.

---

# How to have data arranged by the ascending order of bill length of penguins?

---

```r
penguins %>% 
* arrange(bill_length_mm)
```
]

```
## # A tibble: 344 × 8
##    species island    bill_length_mm bill_depth_mm flipper_…¹ body_…² sex    year
##    <fct>   <fct>              <dbl>         <dbl>      <int>   <int> <fct> <int>
##  1 Adelie  Dream               32.1          15.5        188    3050 fema…  2009
##  2 Adelie  Dream               33.1          16.1        178    2900 fema…  2008
##  3 Adelie  Torgersen           33.5          19          190    3600 fema…  2008
##  4 Adelie  Dream               34            17.1        185    3400 fema…  2008
##  5 Adelie  Torgersen           34.1          18.1        193    3475 <NA>   2007
##  6 Adelie  Torgersen           34.4          18.4        184    3325 fema…  2007
##  7 Adelie  Biscoe              34.5          18.1        187    2900 fema…  2008
##  8 Adelie  Torgersen           34.6          21.1        198    4400 male   2007
##  9 Adelie  Torgersen           34.6          17.2        189    3200 fema…  2008
## 10 Adelie  Biscoe              35            17.9        190    3450 fema…  2008
## # … with 334 more rows, and abbreviated variable names ¹flipper_length_mm,
## #   ²body_mass_g
```

]
]

---

```r
penguins %>% 
* arrange(desc(bill_length_mm))
```
]

```
## # A tibble: 344 × 8
##    species   island bill_length_mm bill_depth_mm flipper_l…¹ body_…² sex    year
##    <fct>     <fct>           <dbl>         <dbl>       <int>   <int> <fct> <int>
##  1 Gentoo    Biscoe           59.6          17           230    6050 male   2007
##  2 Chinstrap Dream            58            17.8         181    3700 fema…  2007
##  3 Gentoo    Biscoe           55.9          17           228    5600 male   2009
##  4 Chinstrap Dream            55.8          19.8         207    4000 male   2009
##  5 Gentoo    Biscoe           55.1          16           230    5850 male   2009
##  6 Gentoo    Biscoe           54.3          15.7         231    5650 male   2008
##  7 Chinstrap Dream            54.2          20.8         201    4300 male   2008
##  8 Chinstrap Dream            53.5          19.9         205    4500 male   2008
##  9 Gentoo    Biscoe           53.4          15.8         219    5500 male   2009
## 10 Chinstrap Dream            52.8          20           205    4550 male   2008
## # … with 334 more rows, and abbreviated variable names ¹flipper_length_mm,
## #   ²body_mass_g
```

]
]

---

```r
penguins %>% 
  arrange(species)
```
]

```
## # A tibble: 344 × 8
##    species island    bill_length_mm bill_depth_mm flipper_…¹ body_…² sex    year
##    <fct>   <fct>              <dbl>         <dbl>      <int>   <int> <fct> <int>
##  1 Adelie  Torgersen           39.1          18.7        181    3750 male   2007
##  2 Adelie  Torgersen           39.5          17.4        186    3800 fema…  2007
##  3 Adelie  Torgersen           40.3          18          195    3250 fema…  2007
##  4 Adelie  Torgersen           NA            NA           NA      NA <NA>   2007
##  5 Adelie  Torgersen           36.7          19.3        193    3450 fema…  2007
##  6 Adelie  Torgersen           39.3          20.6        190    3650 male   2007
##  7 Adelie  Torgersen           38.9          17.8        181    3625 fema…  2007
##  8 Adelie  Torgersen           39.2          19.6        195    4675 male   2007
##  9 Adelie  Torgersen           34.1          18.1        193    3475 <NA>   2007
## 10 Adelie  Torgersen           42            20.2        190    4250 <NA>   2007
## # … with 334 more rows, and abbreviated variable names ¹flipper_length_mm,
## #   ²body_mass_g
```

]
]

---

# `summarise()` function

---

# `summarise()` function: Chooses rows based on column values.

---

# How to find mean bill length of all penguins?

---

```r
penguins %>% 
* drop_na() %>%
* summarise(mean_bill_length_mm = mean(bill_length_mm))
```
]

```
## # A tibble: 1 × 1
##   mean_bill_length_mm
##                 <dbl>
## 1                44.0
```

]
]

---

# How to find species-wise mean bill length of penguins?

---

```r
penguins %>% 
* drop_na() %>%
* group_by(species) %>%
  summarise(mean_bill_length_mm = mean(bill_length_mm))
```
]

```
## # A tibble: 3 × 2
##   species   mean_bill_length_mm
##   <fct>                   <dbl>
## 1 Adelie                   38.8
## 2 Chinstrap                48.8
## 3 Gentoo                   47.6
```

]
]

---

# How to find species-wise mean bill length of penguins and total number of penguins in each species?

---

```r
penguins %>% 
  drop_na() %>% 
  group_by(species) %>% 
* summarise(mean_bill_length_mm = mean(bill_length_mm), n = n())
```
]

```
## # A tibble: 3 × 3
##   species   mean_bill_length_mm     n
##   <fct>                   <dbl> <int>
## 1 Adelie                   38.8   146
## 2 Chinstrap                48.8    68
## 3 Gentoo                   47.6   119
```

]
]

---

#  🙋🏽‍♀️🙋‍♂️<br>.big-text[Q&A]