Work on ex02

ex02_create-or-mutate-in-place.R

@@ -1,5 +1,5 @@
 #' ---
-#' title: "How to add or modify a variable"
+#' title: "Add or modify a variable"
 #' author: "Jenny Bryan"
 #' date: "`r format(Sys.Date())`"
 #' output: github_document
@@ -18,51 +18,64 @@ options(tidyverse.quiet = TRUE)
 library(tidyverse)
 
 # ----
-#' ## Function to give my example data frame
+#' ### Function to produce a fresh example data frame
 new_df <- function() {
   tribble(
     ~ name, ~ age,
-    "Reed", 14,
-    "Wesley", 12,
-    "Eli", 12,
-    "Toby", 1
+    "Reed", 14L,
+    "Wesley", 12L,
+    "Eli", 12L,
+    "Toby", 1L
   )
 }
 
 # ----
 #' ## The `df$var <- ...` syntax
 
-#' This absolutely works. But there are downsides:
+#' How to create or modify a variable is a fairly low stakes matter, i.e. really
+#' a matter of taste. This is not a hill I plan to die on. But here's my two
+#' cents.
+#'
+#' Of course, `df$var <- ...` absolutely works for creating new variables or
+#' modifying existing ones. But there are downsides:
 #'
 #'   * Silent recycling is a risk.
 #'   * `df` is not special. It's not the implied place to look first for things,
-#'   so you must be explicit.
+#'   so you must be explicit. This can be a drag.
 #'   * I have aesthetic concerns. YMMV.
 df <- new_df()
-df$legs <- 4
+df$eyes <- 2L
 df$snack <- c("chips", "cheese")
 df$uname <- toupper(df$name)
 df
 
 # ----
 #' ## `dplyr::mutate()` works "inside the box"
 
-#' `dplyr::mutate()` is the tidyverse way to work on a variable:
+#' `dplyr::mutate()` is the tidyverse way to work on a variable. If I'm working
+#' in a script-y style and the tidyverse packages are already available, I
+#' generally prefer this method of adding or modifying a variable.
 #'
 #'   * Only a length one input can be recycled.
 #'   * `df` is the first place to look for things. It turns out that making a
-#'   new variable out of existing variables is very, very common.
+#'   new variable out of existing variables is very, very common, so it's nice
+#'   when this is easy.
+#'   * This is pipe-friendly, so I can easily combine with a few other logical
+#'   data manipuluations that need to happen around the same point.
 #'   * I like the way this looks. YMMV.
-df <- new_df()
-df %>%
+
+new_df() %>%
   mutate(
-    legs = 4,
+    eyes = 2L,
     snack = c("chips", "cheese"),
     uname = toupper(name)
   )
-df %>%
+
+#' Oops! I did not provide enough snacks!
+
+new_df() %>%
   mutate(
-    legs = 4,
+    eyes = 2L,
     snack = c("chips", "cheese", "mixed nuts", "nerf bullets"),
     uname = toupper(name)
   )

ex02_create-or-mutate-in-place.md

@@ -1,4 +1,4 @@
-How to add or modify a variable
+Add or modify a variable
 ================
 Jenny Bryan
 2018-04-02
@@ -7,77 +7,93 @@ Jenny Bryan
 library(tidyverse)
 ```
 
-## Function to give my example data frame
+### Function to produce a fresh example data frame
 
 ``` r
 new_df <- function() {
   tribble(
     ~ name, ~ age,
-    "Reed", 14,
-    "Wesley", 12,
-    "Eli", 12,
-    "Toby", 1
+    "Reed", 14L,
+    "Wesley", 12L,
+    "Eli", 12L,
+    "Toby", 1L
   )
 }
 ```
 
 ## The `df$var <- ...` syntax
 
-This absolutely works. But there are downsides:
+How to create or modify a variable is a fairly low stakes matter,
+i.e. really a matter of taste. This is not a hill I plan to die on. But
+here’s my two cents.
+
+Of course, `df$var <- ...` absolutely works for creating new variables
+or modifying existing ones. But there are downsides:
 
   - Silent recycling is a risk.
   - `df` is not special. It’s not the implied place to look first for
-    things, so you must be explicit.
+    things, so you must be explicit. This can be a drag.
   - I have aesthetic concerns. YMMV.
 
 <!-- end list -->
 
 ``` r
 df <- new_df()
-df$legs <- 4
+df$eyes <- 2L
 df$snack <- c("chips", "cheese")
 df$uname <- toupper(df$name)
 df
 #> # A tibble: 4 x 5
-#>   name     age  legs snack  uname 
-#>   <chr>  <dbl> <dbl> <chr>  <chr> 
-#> 1 Reed     14.    4. chips  REED  
-#> 2 Wesley   12.    4. cheese WESLEY
-#> 3 Eli      12.    4. chips  ELI   
-#> 4 Toby      1.    4. cheese TOBY
+#>   name     age  eyes snack  uname 
+#>   <chr>  <int> <int> <chr>  <chr> 
+#> 1 Reed      14     2 chips  REED  
+#> 2 Wesley    12     2 cheese WESLEY
+#> 3 Eli       12     2 chips  ELI   
+#> 4 Toby       1     2 cheese TOBY
 ```
 
 ## `dplyr::mutate()` works “inside the box”
 
-`dplyr::mutate()` is the tidyverse way to work on a variable:
+`dplyr::mutate()` is the tidyverse way to work on a variable. If I’m
+working in a script-y style and the tidyverse packages are already
+available, I generally prefer this method of adding or modifying a
+variable.
 
   - Only a length one input can be recycled.
   - `df` is the first place to look for things. It turns out that making
-    a new variable out of existing variables is very, very common.
+    a new variable out of existing variables is very, very common, so
+    it’s nice when this is easy.
+  - This is pipe-friendly, so I can easily combine with a few other
+    logical data manipuluations that need to happen around the same
+    point.
   - I like the way this looks. YMMV.
 
 <!-- end list -->
 
 ``` r
-df <- new_df()
-df %>%
+new_df() %>%
   mutate(
-    legs = 4,
+    eyes = 2L,
     snack = c("chips", "cheese"),
     uname = toupper(name)
   )
 #> Error in mutate_impl(.data, dots): Column `snack` must be length 4 (the number of rows) or one, not 2
-df %>%
+```
+
+Oops\! I did not provide enough snacks\!
+
+``` r
+new_df() %>%
   mutate(
-    legs = 4,
+    eyes = 2L,
     snack = c("chips", "cheese", "mixed nuts", "nerf bullets"),
     uname = toupper(name)
   )
 #> # A tibble: 4 x 5
-#>   name     age  legs snack        uname 
-#>   <chr>  <dbl> <dbl> <chr>        <chr> 
-#> 1 Reed     14.    4. chips        REED  
-#> 2 Wesley   12.    4. cheese       WESLEY
-#> 3 Eli      12.    4. mixed nuts   ELI   
-#> 4 Toby      1.    4. nerf bullets TOBY
+#>   name     age  eyes snack        uname 
+#>   <chr>  <int> <int> <chr>        <chr> 
+#> 1 Reed      14     2 chips        REED  
+#> 2 Wesley    12     2 cheese       WESLEY
+#> 3 Eli       12     2 mixed nuts   ELI   
+#> 4 Toby       1     2 nerf bullets TOBY
 ```