Why doesn't gather() use the key variable name?

问题

It's shameful, but I still can't wrap my mind fully around tidyr, specifically gather(). I feel like I'm missing something fundamental.

If I run this tiny snippet of code

library(tidyr)
x <- data.frame(var1=letters[1:3], var2=LETTERS[7:9], var3=21:23)
gather(x, foo, value)

I get

> x
  var1 var2 var3
1    a    G   21
2    b    H   22
3    c    I   23

> gather(x, foo, value)
  variable value
1     var1     a
2     var1     b
3     var1     c
4     var2     G
5     var2     H
6     var2     I
7     var3    21
8     var3    22
9     var3    23

Where does foo get used? Is this completely unnecessary? Am I tripping up because I'm thinking reshape style where you define the ID variables and the rest get melted whereas I should be thinking differently where you define the variables to gather and the rest are considered ID?

回答1:

This is a bug that occurs when reshape and tidyr are both loaded. It has been fixed in tidyr 0.3.1.

来源：https://stackoverflow.com/questions/32598113/why-doesnt-gather-use-the-key-variable-name