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Bit more about :=

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Hadley Wickham
2022-12-08 14:47:46 -06:00
parent 5af95dd185
commit 34bb0a5f44
1 changed files with 6 additions and 2 deletions
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functions.qmd
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@@ -737,7 +737,7 @@ diamonds |> hex_plot(carat, price, depth)
Some of the most useful helpers combine a dash of dplyr with ggplot2. Some of the most useful helpers combine a dash of dplyr with ggplot2.
For example, if you might want to do a vertical bar chart where you automatically sort the bars in frequency order using `fct_infreq()`. For example, if you might want to do a vertical bar chart where you automatically sort the bars in frequency order using `fct_infreq()`.
Since the bar chart is vertical, we also need to reverse the usual order to get the highest values at the top (also note the `:=` operator, which allows you to inject names with glue syntax on the left-hand side of ⁠`:=`;⁠ type: ?\`:=\` for more details): Since the bar chart is vertical, we also need to reverse the usual order to get the highest values at the top:
```{r} ```{r}
sorted_bars <- function(df, var) { sorted_bars <- function(df, var) {
@@ -750,6 +750,10 @@ sorted_bars <- function(df, var) {
diamonds |> sorted_bars(cut) diamonds |> sorted_bars(cut)
``` ```
We have to use a new operator here, `:=`, because we are generating the variable name based on user-supplied data.
Variable names go on the left hand side of `=`, but R's syntax doesn't allow anything to the left of `=` except for a single literal name.
To work around this problem, we use the special operator `:=` which tidy evaluation treats in exactly the same way as `=`.
Or maybe you want to make it easy to draw a bar plot just for a subset of the data: Or maybe you want to make it easy to draw a bar plot just for a subset of the data:
```{r} ```{r}
@@ -938,7 +942,7 @@ This makes it very obvious that something unusual is happening.
f1 <- function(string, prefix) { f1 <- function(string, prefix) {
substr(string, 1, nchar(prefix)) == prefix substr(string, 1, nchar(prefix)) == prefix
} }
f3 <- function(x, y) { f3 <- function(x, y) {
rep(y, length.out = length(x)) rep(y, length.out = length(x))
} }