---
title: "Drawing graphs"
editor: 
  markdown: 
    wrap: 72
---

## Our data

-   To illustrate making graphs, we need some data.
-   Data on 202 male and female athletes at the Australian Institute of
    Sport.
-   Variables:
    -   categorical: Sex of athlete, sport they play
    -   quantitative: height (cm), weight (kg), lean body mass, red and
        white blood cell counts, haematocrit and haemoglobin (blood),
        ferritin concentration, body mass index, percent body fat.
-   Values separated by tabs (which impacts reading in).

## Packages for this section

```{r graphs-R-1}
library(tidyverse)
```

## Reading data into R

-   Use `read_tsv` ("tab-separated values"), like `read_csv`.
-   Data in `ais.txt`:

```{r graphs-R-2}
my_url <- "http://ritsokiguess.site/datafiles/ais.txt"
athletes <- read_tsv(my_url)
```

## The data (some)

```{r graphs-R-3}
athletes
```

## Types of graph {.smaller}

Depends on number and type of variables:

| Categorical | Quantitative | Graph                                                       |
|-------------:|-------------:|:-------------------------------------------|
|           1 |            0 | bar chart                                                   |
|           0 |            1 | histogram                                                   |
|           2 |            0 | grouped bar charts                                          |
|           1 |            1 | side-by-side boxplots                                       |
|           0 |            2 | scatterplot                                                 |
|           2 |            1 | grouped boxplots                                            |
|           1 |            2 | scatterplot with points identified by group (eg. by colour) |

With more (categorical) variables, might want *separate plots by
groups*. This is called `facetting` in R.

## `ggplot`

-   R has a standard graphing procedure `ggplot`, that we use for all
    our graphs.
-   Use in different ways to get precise graph we want.
-   Let's start with bar chart of the sports played by the athletes.

## Bar chart

```{r graphs-R-4, fig.height=3.9}
ggplot(athletes, aes(x = Sport)) + geom_bar()
```

## Histogram of body mass index

```{r graphs-R-5, fig.height=3.9}
ggplot(athletes, aes(x = BMI)) + geom_histogram(bins = 16)
```

## Which sports are played by males and females?

Grouped bar chart:

```{r graphs-R-6, fig.height=3.15}
ggplot(athletes, aes(x = Sport, fill = Sex)) +
  geom_bar(position = "dodge")
```

## BMI by gender

```{r graphs-R-7, fig.height=4}
ggplot(athletes, aes(x = Sex, y = BMI)) + geom_boxplot() 
```

## Height vs. weight

Scatterplot:

```{r graphs-R-8, fig.height=3.4}
ggplot(athletes, aes(x = Ht, y = Wt)) + geom_point()
```

## With regression line

```{r graphs-R-9, fig.height=3.6}
ggplot(athletes, aes(x = Ht, y = Wt)) +
  geom_point() + geom_smooth(method = "lm")
```

## BMI by sport and gender

```{r graphs-R-10, fig.height=3.6}
ggplot(athletes, aes(x = Sport, y = BMI, fill = Sex)) +
  geom_boxplot()
```

A variation that uses `colour` instead of `fill`:

```{r}
ggplot(athletes, aes(x = Sport, y = BMI, colour = Sex)) +
  geom_boxplot()
```

## Height and weight by gender

```{r}
#| fig-height: 9
#| fig-width: 9
ggplot(athletes, aes(x = Ht, y = Wt, colour = Sex)) +
  geom_point()
```

## Height by weight by gender for each sport, with facets

```{r graphs-R-12, fig.height=3.6}
ggplot(athletes, aes(x = Ht, y = Wt, colour = Sex)) +
  geom_point() + facet_wrap(~Sport)
```

## Filling each facet

Default uses same scale for each facet. To use different scales for each
facet, this:

```{r graphs-R-13, fig.height=5.2}
ggplot(athletes, aes(x = Ht, y = Wt, colour = Sex)) +
  geom_point() + facet_wrap(~Sport, scales = "free")
```

## Another view of height vs weight

```{r}
ggplot(athletes, aes(x = Ht, y = Wt)) +
  geom_point() + facet_wrap(~ Sex)
```