Visualizing data with ggplot2 🎨

---

layout: true
  
<div class="my-footer">
<span>
<a href="https://DataScience4Psych.github.io/DataScience4Psych/" target="_blank">Data Science for Psychologists</a>
</span>
</div>

---

# ggplot2 ❤️ 🐧

---

## ggplot2 `$\in$` tidyverse

.pull-left-narrow[
<img src="img/ggplot2-part-of-tidyverse.png" width="60%" style="display: block; margin: auto;" />
] 
.pull-right-wide[ 
- **ggplot2** is tidyverse's data visualization package 
- Structure of the code for plots can be summarized as

```r
ggplot(data = [dataset], 
     mapping = aes(x = [x-variable], 
                   y = [y-variable])) +
   geom_xxx() +
   other options
```
]

---

## Data: Palmer Penguins

.pull-right[
+ Measurements for penguin species, 
  + island in Palmer Archipelago, 
  + size (flipper length, body mass, bill dimensions), and 
  + sex.
]
---

## Data: Palmer Penguins

Measurements for penguin species, island in Palmer Archipelago, size (flipper length, body mass, bill dimensions), and sex.

```r
library(palmerpenguins)
glimpse(penguins)
```

```
## Rows: 344
## Columns: 8
## $ species           <fct> Adelie, Adelie, Adelie, Adelie, Adeli…
## $ island            <fct> Torgersen, Torgersen, Torgersen, Torg…
## $ bill_length_mm    <dbl> 39.1, 39.5, 40.3, NA, 36.7, 39.3, 38.…
## $ bill_depth_mm     <dbl> 18.7, 17.4, 18.0, NA, 19.3, 20.6, 17.…
## $ flipper_length_mm <int> 181, 186, 195, NA, 193, 190, 181, 195…
## $ body_mass_g       <int> 3750, 3800, 3250, NA, 3450, 3650, 362…
## $ sex               <fct> male, female, female, NA, female, mal…
## $ year              <int> 2007, 2007, 2007, 2007, 2007, 2007, 2…
```

---

# Plot

---

# Code

```
## Warning: Removed 2 rows containing missing values
## (`geom_point()`).
```

---
class: middle

# Coding out loud

---

```r
*ggplot(data = penguins)
```
]
.pull-right-narrow[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-7-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
*      mapping = aes(x = bill_depth_mm))
```
]
.pull-right-narrow[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-8-1.png" width="100%" style="display: block; margin: auto;" />
]

---

.midi[
> Start with the `penguins` data frame,
> map bill depth to the x-axis
> **and map bill length to the y-axis.**
]

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
*                    y = bill_length_mm))
```
]
.pull-right-narrow[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-9-1.png" width="100%" style="display: block; margin: auto;" />
]

---

.midi[
> Start with the `penguins` data frame,
> map bill depth to the x-axis
> and map bill length to the y-axis. 
> **Represent each observation with a point**
]

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm)) + 
* geom_point()
```
]
.pull-right-narrow[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-10-1.png" width="100%" style="display: block; margin: auto;" />
]

---

.midi[
> Start with the `penguins` data frame,
> map bill depth to the x-axis
> and map bill length to the y-axis. 
> Represent each observation with a point
> **and map species to the color of each point.**
]

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
*                    color = species)) +
  geom_point()
```
]
.pull-right-narrow[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-11-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
* labs(title = "Bill depth and length")
```
]
.pull-right-narrow[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-12-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  labs(title = "Bill depth and length",
*      subtitle = "Dimensions for Adelie, Chinstrap, and Gentoo Penguins")
```
]
.pull-right-narrow[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-13-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  labs(title = "Bill depth and length",
       subtitle = "Dimensions for Adelie, Chinstrap, and Gentoo Penguins",
*      x = "Bill depth (mm)", y = "Bill length (mm)")
```
]
.pull-right-narrow[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-14-1.png" width="100%" style="display: block; margin: auto;" />
]

---

.midi[
> Start with the `penguins` data frame,
> map bill depth to the x-axis
> and map bill length to the y-axis. 
> Represent each observation with a point
> and map species to the color of each point.
> Title the plot "Bill depth and length", 
> add the subtitle "Dimensions for Adelie, Chinstrap, and Gentoo Penguins", 
> label the x and y axes as "Bill depth (mm)" and "Bill length (mm)", respectively,
> **label the legend "Species"**
]

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  labs(title = "Bill depth and length",
       subtitle = "Dimensions for Adelie, Chinstrap, and Gentoo Penguins",
       x = "Bill depth (mm)", y = "Bill length (mm)",
*      color = "Species")
```
]
.pull-right-narrow[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-15-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  labs(title = "Bill depth and length",
       subtitle = "Dimensions for Adelie, Chinstrap, and Gentoo Penguins",
       x = "Bill depth (mm)", y = "Bill length (mm)",
       color = "Species",
*      caption = "Source: Palmer Station LTER / palmerpenguins package")
```
]
.pull-right-narrow[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-16-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  labs(title = "Bill depth and length",
       subtitle = "Dimensions for Adelie, Chinstrap, and Gentoo Penguins",
       x = "Bill depth (mm)", y = "Bill length (mm)",
       color = "Species",
       caption = "Source: Palmer Station LTER / palmerpenguins package") +
* scale_color_viridis_d()
```
]
.pull-right-narrow[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-17-1.png" width="100%" style="display: block; margin: auto;" />
]

---

# Plot

---

# Code

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  labs(title = "Bill depth and length",
       subtitle = "Dimensions for Adelie, Chinstrap, and Gentoo Penguins",
       x = "Bill depth (mm)", y = "Bill length (mm)",
       color = "Species",
       caption = "Source: Palmer Station LTER / palmerpenguins package") +
  scale_color_viridis_d()
```

---

# Narrative

.medi[
+ Start with the `penguins` data frame,
map bill depth to the x-axis
and map bill length to the y-axis. 
+ Represent each observation with a point
and map species to the color of each point.
+ Title the plot "Bill depth and length", 
add the subtitle "Dimensions for Adelie, Chinstrap, and Gentoo Penguins", 
label the x and y axes as "Bill depth (mm)" and "Bill length (mm)", respectively,
label the legend "Species", 
and add a caption for the data source.
+ Finally, use a discrete color scale that is designed to be perceived by viewers with common forms of color blindness.
]

---

# Coding out loud (larger graphics)

---

```r
*ggplot(data = penguins)
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-19-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
*      mapping = aes(x = bill_depth_mm))
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-20-1.png" width="100%" style="display: block; margin: auto;" />
]

---

.midi[
> Start with the `penguins` data frame,
> map bill depth to the x-axis
> **and map bill length to the y-axis.**
]

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
*                    y = bill_length_mm))
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-21-1.png" width="100%" style="display: block; margin: auto;" />
]

---

.midi[
> Start with the `penguins` data frame,
> map bill depth to the x-axis
> and map bill length to the y-axis. 
> **Represent each observation with a point**
]

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm)) + 
* geom_point()
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-22-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
*                    color = species)) +
  geom_point()
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-23-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
* labs(title = "Bill depth and length")
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-24-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  labs(title = "Bill depth and length",
*      subtitle = "Dimensions for Adelie, Chinstrap, and Gentoo Penguins")
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-25-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  labs(title = "Bill depth and length",
       subtitle = "Dimensions for Adelie, Chinstrap, and Gentoo Penguins",
*      x = "Bill depth (mm)", y = "Bill length (mm)")
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-26-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  labs(title = "Bill depth and length",
       subtitle = "Dimensions for Adelie, Chinstrap, and Gentoo Penguins",
       x = "Bill depth (mm)", y = "Bill length (mm)",
*      color = "Species")
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-27-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  labs(title = "Bill depth and length",
       subtitle = "Dimensions for Adelie, Chinstrap, and Gentoo Penguins",
       x = "Bill depth (mm)", y = "Bill length (mm)",
       color = "Species",
*      caption = "Source: Palmer Station LTER / palmerpenguins package")
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-28-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  labs(title = "Bill depth and length",
       subtitle = "Dimensions for Adelie, Chinstrap, and Gentoo Penguins",
       x = "Bill depth (mm)", y = "Bill length (mm)",
       color = "Species",
       caption = "Source: Palmer Station LTER / palmerpenguins package") +
* scale_color_viridis_d()
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-29-1.png" width="100%" style="display: block; margin: auto;" />
]

---

## Argument names

```r
ggplot(data = penguins,
       mapping = aes(x = bill_depth_mm,
                     y = bill_length_mm,
                     color = species)) +
  geom_point() +
  scale_color_viridis_d()
```
]
.pull-right[

```r
ggplot(penguins,
       aes(x = bill_depth_mm,
           y = bill_length_mm,
           color = species)) +
  geom_point() +
  scale_color_viridis_d()
```
]

---

# Wrapping Up...

---

# Aesthetics

---

## Aesthetics options

Commonly used characteristics of plotting characters that can be **mapped to a specific variable** in the data are

- `color`
- `shape`
- `size`
- `alpha` (transparency)

---

## Color

```r
ggplot(penguins,
       aes(x = bill_depth_mm, 
           y = bill_length_mm,
*          color = species)) +
  geom_point() +
  scale_color_viridis_d()
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-30-1.png" width="100%" style="display: block; margin: auto;" />
]

---

## Shape

Mapped to a different variable than `color`

```r
ggplot(penguins,
       aes(x = bill_depth_mm, 
           y = bill_length_mm,
           color = species,
*          shape = island)) +
  geom_point() +
  scale_color_viridis_d()
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-31-1.png" width="100%" style="display: block; margin: auto;" />
]

---

## Shape

Mapped to same variable as `color`

```r
ggplot(penguins,
       aes(x = bill_depth_mm, 
           y = bill_length_mm,
           color = species,
*          shape = species)) +
  geom_point() +
  scale_color_viridis_d()
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-32-1.png" width="100%" style="display: block; margin: auto;" />
]

---

## Size

```r
ggplot(penguins,
       aes(x = bill_depth_mm, 
           y = bill_length_mm,
           color = species,
           shape = species,
*          size = body_mass_g)) +
  geom_point() +
  scale_color_viridis_d()
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-33-1.png" width="100%" style="display: block; margin: auto;" />
]

---

## Alpha

```r
ggplot(penguins,
       aes(x = bill_depth_mm, 
           y = bill_length_mm,
           color = species,
           shape = species,
           size = body_mass_g,
*          alpha = flipper_length_mm)) +
  geom_point() +
  scale_color_viridis_d()
```
]
.pull-right[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-34-1.png" width="100%" style="display: block; margin: auto;" />
]

---

```r
ggplot(penguins,
      aes(x = bill_depth_mm,
          y = bill_length_mm,
*         size = body_mass_g,
*         alpha = flipper_length_mm))+
  geom_point()
```

<img src="d04_ggplot2_files/figure-html/unnamed-chunk-35-1.png" width="100%" style="display: block; margin: auto;" />
]]
.pull-right[
**Setting**
.medi[

```r
ggplot(penguins,
       aes(x = bill_depth_mm,
           y = bill_length_mm)) + 
* geom_point(size = 2, alpha = 0.5)
```

<img src="d04_ggplot2_files/figure-html/unnamed-chunk-36-1.png" width="100%" style="display: block; margin: auto;" />
]
]
---

## Mapping vs. setting

- **Mapping:** Determine the size, alpha, etc. of points based on the values of a variable in the data
  - goes into `aes()`
- **Setting:** Determine the size, alpha, etc. of points **not** based on the values of a variable in the data
  - goes into `geom_*()` 
     - (in the previous example, we used `geom_point()` , 
         - but we'll learn about other geoms soon!)
  
---

# Faceting

---

## Faceting

- Smaller plots that display different subsets of the data
- Useful for exploring conditional relationships and large data

---

### Plot
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-37-1.png" width="70%" style="display: block; margin: auto;" />

---

### Code

```r
ggplot(penguins, aes(x = bill_depth_mm, y = bill_length_mm)) + 
  geom_point() +
* facet_grid(species ~ island)
```

---

## Various ways to facet

In the next few slides, describe what each plot displays. Think about how the code relates to the output.

.question[
**Note:** The plots in the next few slides do not have proper titles, axis labels, etc. because I want you to figure out what's happening in the plots.
But you should always label your plots!
]

---

```r
ggplot(penguins, aes(x = bill_depth_mm, y = bill_length_mm)) + 
  geom_point() +
* facet_grid(species ~ sex)
```

---

```r
ggplot(penguins, aes(x = bill_depth_mm, y = bill_length_mm)) + 
  geom_point() +
* facet_grid(sex ~ species)
```

---

```r
ggplot(penguins, aes(x = bill_depth_mm, y = bill_length_mm)) + 
  geom_point() +
* facet_wrap(~ species)
```

---

```r
ggplot(penguins, aes(x = bill_depth_mm, y = bill_length_mm)) + 
  geom_point() +
* facet_grid(. ~ species)
```

---

```r
ggplot(penguins, aes(x = bill_depth_mm, y = bill_length_mm)) + 
  geom_point() +
* facet_wrap(~ species, ncol = 2)
```

---

## Faceting summary  (Facinating...)

- Faceting allows you to create multiple plots based on a factor variable, which are then displayed in a grid.
- **`facet_grid()`**:
    - Creates a 2D grid of plots, one for each level of two factor variables.
    - The format is `rows ~ cols`.
    - Use `.` if there is no variable to split in either the row or column direction.
- **`facet_wrap()`**:
    - Creates a 1D ribbon of plots, each for a level of one factor variable.
    - Plots are wrapped into a grid that respects the number of rows and columns specified or the available plotting area.
    - Ideal when there's only one factor variable, or for multi-level factors.

---

## Facet and color

```r
ggplot(
  penguins, 
  aes(x = bill_depth_mm, 
      y = bill_length_mm, 
*     color = species)) +
  geom_point() +
  facet_grid(species ~ sex) +
* scale_color_viridis_d()
```
]
.pull-right-wide[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-43-1.png" width="100%" style="display: block; margin: auto;" />
]

---

## Facet and color, no legend

```r
ggplot(
  penguins, 
  aes(x = bill_depth_mm, 
      y = bill_length_mm, 
      color = species)) +
  geom_point() +
  facet_grid(species ~ sex) +
  scale_color_viridis_d() +
* guides(color = FALSE)
```
]
.pull-right-wide[
<img src="d04_ggplot2_files/figure-html/unnamed-chunk-44-1.png" width="100%" style="display: block; margin: auto;" />
]

---

# Wrapping Up...