Data types

# Data types
## <br><br> Introduction to Data Science with R and Tidyverse
### based on datasciencebox.org

---

layout: true
  
<div class="my-footer">
<span>
Introduction to Data Science with R and Tidyverse | Lukas Jürgensmeier, Matteo Fina, Jan Bischoff | based on
<a href="https://datasciencebox.org" target="_blank">datasciencebox.org</a>
</span>
</div>

---

# Why should you care about data types?

---

## Example: Cat lovers

A survey asked respondents their name and number of cats. The instructions said to enter the number of cats as a numerical value.

```r
cat_lovers <- read_csv("data/cat-lovers.csv")
```

```
## # A tibble: 60 x 3
##   name           number_of_cats handedness
##   <chr>          <chr>          <chr>     
## 1 Bernice Warren 0              left      
## 2 Woodrow Stone  0              left      
## 3 Willie Bass    1              left      
## 4 Tyrone Estrada 3              left      
## 5 Alex Daniels   3              left      
## 6 Jane Bates     2              left      
## # ... with 54 more rows
```

---

## Oh why won't you work?!

```r
cat_lovers %>%
  summarise(mean_cats = mean(number_of_cats))
```

```
## Warning: There was 1 warning in `summarise()`.
## i In argument: `mean_cats = mean(number_of_cats)`.
## Caused by warning in `mean.default()`:
## ! argument is not numeric or logical: returning NA
```

```
## # A tibble: 1 x 1
##   mean_cats
##       <dbl>
## 1        NA
```

---

```r
?mean
```

---

## Oh why won't you still work??!!

```r
cat_lovers %>%
  summarise(mean_cats = mean(number_of_cats, na.rm = TRUE))
```

```
## Warning: There was 1 warning in `summarise()`.
## i In argument: `mean_cats = mean(number_of_cats, na.rm = TRUE)`.
## Caused by warning in `mean.default()`:
## ! argument is not numeric or logical: returning NA
```

```
## # A tibble: 1 x 1
##   mean_cats
##       <dbl>
## 1        NA
```

---

## Take a breath and look at your data

```r
glimpse(cat_lovers)
```

```
## Rows: 60
## Columns: 3
## $ name           <chr> "Bernice Warren", "Woodrow Stone", "Will~
## $ number_of_cats <chr> "0", "0", "1", "3", "3", "2", "1", "1", ~
## $ handedness     <chr> "left", "left", "left", "left", "left", ~
```

---

## Let's take another look

Check out the responses from "Ginger Clark" and "Doug Bass"

.small[
<div id="htmlwidget-1b4ff99564eb6e8884a5" style="width:100%;height:auto;" class="datatables html-widget"></div>
<script type="application/json" data-for="htmlwidget-1b4ff99564eb6e8884a5">{"x":{"filter":"none","vertical":false,"data":[["1","2","3","4","5","6","7","8","9","10","11","12","13","14","15","16","17","18","19","20","21","22","23","24","25","26","27","28","29","30","31","32","33","34","35","36","37","38","39","40","41","42","43","44","45","46","47","48","49","50","51","52","53","54","55","56","57","58","59","60"],["Bernice Warren","Woodrow Stone","Willie Bass","Tyrone Estrada","Alex Daniels","Jane Bates","Latoya Simpson","Darin Woods","Agnes Cobb","Tabitha Grant","Perry Cross","Wanda Silva","Alicia Sims","Emily Logan","Woodrow Elliott","Brent Copeland","Pedro Carlson","Patsy Luna","Brett Robbins","Oliver George","Calvin Perry","Lora Gutierrez","Charlotte Sparks","Earl Mack","Leslie Wade","Santiago Barker","Jose Bell","Lynda Smith","Bradford Marshall","Irving Miller","Caroline Simpson","Frances Welch","Melba Jenkins","Veronica Morales","Juanita Cunningham","Maurice Howard","Teri Pierce","Phil Franklin","Jan Zimmerman","Leslie Price","Bessie Patterson","Ethel Wolfe","Naomi Wright","Sadie Frank","Lonnie Cannon","Tony Garcia","Darla Newton","Ginger Clark","Lionel Campbell","Florence Klein","Harriet Leonard","Terrence Harrington","Travis Garner","Doug Bass","Pat Norris","Dawn Young","Shari Alvarez","Tamara Robinson","Megan Morgan","Kara Obrien"],["0","0","1","3","3","2","1","1","0","0","0","0","1","3","3","2","1","1","0","0","1","1","0","0","4","0","0","0","0","0","0","0","0","0","0","0","0","0","0","0","0","0","1","3","3","2","1","1.5 - honestly I think one of my cats is half human","0","0","1","0","1","three","1","1","1","0","0","2"],["left","left","left","left","left","left","left","left","left","left","left","left","left","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","right","ambidextrous","ambidextrous","ambidextrous","ambidextrous","ambidextrous"]],"container":"<table class=\"display\">\n  <thead>\n    <tr>\n      <th> <\/th>\n      <th>name<\/th>\n      <th>number_of_cats<\/th>\n      <th>handedness<\/th>\n    <\/tr>\n  <\/thead>\n<\/table>","options":{"order":[],"autoWidth":false,"orderClasses":false,"columnDefs":[{"orderable":false,"targets":0}]}},"evals":[],"jsHooks":[]}</script>
]

---

## Sometimes you might need to babysit your respondents

```r
cat_lovers %>%
  mutate(number_of_cats = case_when(
    name == "Ginger Clark" ~ 2,
    name == "Doug Bass"    ~ 3,
    TRUE                   ~ as.numeric(number_of_cats)
    )) %>%
  summarise(mean_cats = mean(number_of_cats))
```

```
## Warning: There was 1 warning in `mutate()`.
## i In argument: `number_of_cats = case_when(...)`.
## Caused by warning:
## ! NAs introduced by coercion
```

```
## # A tibble: 1 x 1
##   mean_cats
##       <dbl>
## 1     0.833
```
]

---

## You always need to respect data types

```r
cat_lovers %>%
  mutate(
    number_of_cats = case_when(
      name == "Ginger Clark" ~ "2",
      name == "Doug Bass"    ~ "3",
      TRUE                   ~ number_of_cats
      ),
    number_of_cats = as.numeric(number_of_cats)
    ) %>%
  summarise(mean_cats = mean(number_of_cats))
```

```
## # A tibble: 1 x 1
##   mean_cats
##       <dbl>
## 1     0.833
```

---

## Now that we know what we're doing...

```r
*cat_lovers <- cat_lovers %>%
  mutate(
    number_of_cats = case_when(
      name == "Ginger Clark" ~ "2",
      name == "Doug Bass"    ~ "3",
      TRUE                   ~ number_of_cats
      ),
    number_of_cats = as.numeric(number_of_cats)
    )
```

---

## Moral of the story

- If your data does not behave how you expect it to, type coercion upon reading in the data might be the reason.
- Go in and investigate your data, apply the fix, *save your data*, live happily ever after.

---

<br>

---

# Data types

---

## Data types in R

- **logical**
- **double**
- **integer**
- **character**
- and some more, but we won't be focusing on those

---

## Logical & character

```r
typeof(TRUE)
```

```
## [1] "logical"
```
]
.pull-right[
**character** - character strings

```r
typeof("hello")
```

```
## [1] "character"
```
]

---

## Double & integer

```r
typeof(1.335)
```

```
## [1] "double"
```

```r
typeof(7)
```

```
## [1] "double"
```
]
.pull-right[
**integer** — integer numerical values (indicated with an `L`)

```r
typeof(7L)
```

```
## [1] "integer"
```

```r
typeof(1:3)
```

```
## [1] "integer"
```
]

---

## Concatenation

Vectors can be constructed using the `c()` function.

```r
c(1, 2, 3)
```

```
## [1] 1 2 3
```

```r
c("Hello", "World!")
```

```
## [1] "Hello"  "World!"
```

```r
c(c("hi", "hello"), c("bye", "jello"))
```

```
## [1] "hi"    "hello" "bye"   "jello"
```

---

## Converting between types

with intention...

```r
x <- 1:3
x
```

```
## [1] 1 2 3
```

```r
typeof(x)
```

```
## [1] "integer"
```
]
--
.pull-right[

```r
y <- as.character(x)
y
```

```
## [1] "1" "2" "3"
```

```r
typeof(y)
```

```
## [1] "character"
```
]

---

## Converting between types

with intention...

```r
x <- c(TRUE, FALSE)
x
```

```
## [1]  TRUE FALSE
```

```r
typeof(x)
```

```
## [1] "logical"
```
]
--
.pull-right[

```r
y <- as.numeric(x)
y
```

```
## [1] 1 0
```

```r
typeof(y)
```

```
## [1] "double"
```
]

---

## Converting between types

without intention...

R will happily convert between various types without complaint when different types of data are concatenated in a vector, and that's not always a great thing!

```r
c(1, "Hello")
```

```
## [1] "1"     "Hello"
```

```r
c(FALSE, 3L)
```

```
## [1] 0 3
```
]
--
.pull-right[

```r
c(1.2, 3L)
```

```
## [1] 1.2 3.0
```

```r
c(2L, "two")
```

```
## [1] "2"   "two"
```
]

---

## Explicit vs. implicit coercion

Let's give formal names to what we've seen so far:

--
- **Explicit coercion** is when you call a function like `as.logical()`, `as.numeric()`, `as.integer()`, `as.double()`, or `as.character()`

--
- **Implicit coercion** happens when you use a vector in a specific context that expects a certain type of vector

---

# Special values

---

## Special values

- `NA`: Not available
- `NaN`: Not a number
- `Inf`: Positive infinity
- `-Inf`: Negative infinity

```r
pi / 0
```

```
## [1] Inf
```

```r
0 / 0
```

```
## [1] NaN
```
]
.pull-right[

```r
1/0 - 1/0
```

```
## [1] NaN
```

```r
1/0 + 1/0
```

```
## [1] Inf
```
]