Reprex.qmd

---
title: "Dynamic Table Captions"
author: "Jon Peake"
format: html
editor: visual
---

## Example 1: from a column value

If the information for our dynamic caption is contained within a column in the dataset (say, a single static column for the species or gear), we can extract the information from the columns of interest. Let's create a dataset with a constant species and gear.

```{r}
#| label: createdata_colval
# Create a dummy dataset
dat <- data.frame(species = rep('Mycteroperca microlepis', 10),
                  gear = rep('Hook and line',10),
                  age = 1:10,
                  size = seq(1,100,10))

write.csv(dat, file = 'dat_colval.csv',row.names = F)
```

We can make a dynamic label in a few ways. If a caption with a similar format is going to be used multiple times throughout the document, it might be easiest to make this a function. Otherwise, we can just use a standard call to `paste`:

```{r}
# Make dynamic label
# read in the data file
dat <- read.csv('dat_colval.csv')

# extract the species name
spp <- unique(dat$species)

# extract the gear
gear <- unique(dat$gear)

# paste together the caption
cap <- paste('Age and length of',
             spp,
             'from',
             gear)
cap
```

We can assign the caption using the `#| tbl-cap` option in our table code chunk. To input an r variable, we use the following notation:

```         
#| tbl-cap: !expr cap
```

By using `!expr` we can insert an R variable or even a full expression into the caption. This example inserts the value of `cap` into the caption.

```{r}
#| label: tbl-colval
#| tbl-cap: !expr cap

# Make table using kable
library(knitr)
kable(dat)
```

## Example 2: from a column header

If instead our dynamic information is in a column header, we can use the `colnames` function to extract the appropriate information. This may be useful if the structure of the data is constant but a value column changes names across datasets.

```{r}
#| label: createdata_colname
# Create a dummy dataset
dat <- data.frame(species = rep('Mycteroperca microlepis', 10),
                  SL = 1:10,
                  FL = 1:10)

write.csv(dat, file = 'dat_colname.csv',row.names = F)
```

```{r}
# Make dynamic label
# read in the data file
dat <- read.csv('dat_colname.csv')

# extract the species name
spp <- unique(dat$species)

# extract the length types
param_1 <- colnames(dat)[2]

param_2 <- colnames(dat)[3]

# paste together the caption
cap <- paste(spp,
             param_1,
             'vs.',
             param_2
             )
cap
```

```{r}
#| label: fig-colname
#| fig-cap: !expr cap

# Make plot using ggplot
library(ggplot2)
ggplot(dat) + geom_point(aes(x = SL, y = FL))
```