Editing Data Into Insights (Spring 2021)/R4DS Chapter 12 (section)

== 12.3 ==

1. Why are pivot_longer() and pivot_wider() not perfectly symmetrical?
Carefully consider the following example:

<syntaxhighlight lang="R">
stocks <- tibble(
  year   = c(2015, 2015, 2016, 2016),
  half  = c(   1,    2,     1,    2),
  return = c(1.88, 0.59, 0.92, 0.17)
)
stocks %>% 
  pivot_wider(names_from = year, values_from = return) %>% 
  pivot_longer(`2015`:`2016`, names_to = "year", values_to = "return")
</syntaxhighlight>

(Hint: look at the variable types and think about column names.)


2. Why does this code fail?

<syntaxhighlight lang="R">
table4a %>% 
  pivot_longer(c(1999, 2000), names_to = "year", values_to = "cases")
#> Error: Can't subset columns that don't exist.
#> ✖ Locations 1999 and 2000 don't exist.
#> ℹ There are only 3 columns.
</syntaxhighlight>

3. What would happen if you widen this table? Why? How could you add a new column to uniquely identify each value?

<syntaxhighlight lang="R">
people <- tribble(
  ~name,             ~variable,  ~value,
  #-----------------|--------|------
  "Phillip Woods",   "age",       45,
  "Phillip Woods",   "height",   186,
  "Phillip Woods",   "age",       50,
  "Jessica Cordero", "age",       37,
  "Jessica Cordero", "height",   156
)
</syntaxhighlight>

4. Tidy the simple tibble below. Do you need to make it wider or longer? What are the variables?

<syntaxhighlight lang="R">
preg <- tribble(
  ~pregnant, ~m, ~f,
  "yes",     NA,    10,
  "no",      20,    12
)
</syntaxhighlight>