Question

我知道如何使用melt的两个id.vars。这很简单：

x = data.frame(subject = c("John", "Mary"), 
               time = c(1,1),
               age = c(33,35),
               weight = c(90, 67),
               height = c(2,2))
melt(x, id.vars = c('subject', 'time'), measure.vars = c('age', 'weight', 'height'))

# subject time variable value
#1    John    1      age    33
#2    Mary    1      age    35
#3    John    1   weight    90
#4    Mary    1   weight    67
#5    John    1   height     2
#6    Mary    1   height     2

但我怎样才能对key使用两个id.vars或gather}？

gather(data, key, value, ..., na.rm = FALSE, convert = FALSE,
  factor_key = FALSE)

我只能设法使用一个key。

Answer 1

您还可以使用-符号指定要保留的变量：

gather(x, variable, value, -c(subject,time))

Answer 2

我们可以通过单独指定列，或者如果它们使用:，或者使用列索引

来执行此操作

library(tidyr)
gather(x, variable, value, age:height)
#    subject time variable value
#1    John    1      age    33
#2    Mary    1      age    35
#3    John    1   weight    90
#4    Mary    1   weight    67
#5    John    1   height     2
#6    Mary    1   height     2

将从melt

提供与reshape2相同的输出

melt(x, id.vars = c('subject', 'time'), measure.vars = c('age', 'weight', 'height'))
#  subject time variable value
#1    John    1      age    33
#2    Mary    1      age    35
#3    John    1   weight    90
#4    Mary    1   weight    67
#5    John    1   height     2
#6    Mary    1   height     2

dplyr：收集两把钥匙

2 个答案: