用 Tidyr 展开多根柱子

以这个样本变量为例

df <- data.frame(month=rep(1:3,2),
student=rep(c("Amy", "Bob"), each=3),
A=c(9, 7, 6, 8, 6, 9),
B=c(6, 7, 8, 5, 6, 7))

我可以使用 spread从 tidyr改变这到广泛的格式。

> df[, -4] %>% spread(student, A)
month Amy Bob
1     1   9   8
2     2   7   6
3     3   6   9

但是如何将两个值(如 A和 B)展开，使得输出类似于

  month Amy.A Bob.A Amy.B Bob.B
1     1     9     8     6     5
2     2     7     6     7     6
3     3     6     9     8     7
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最佳答案

Here's a possible both simple and very efficient solution using data.table 

library(data.table) ## v >= 1.9.6
dcast(setDT(df), month ~ student, value.var = c("A", "B"))
#    month Amy_A Bob_A Amy_B Bob_B
# 1:     1     9     8     6     5
# 2:     2     7     6     7     6
# 3:     3     6     9     8     7

Or a possible tidyr solution

df %>%
gather(variable, value, -(month:student)) %>%
unite(temp, student, variable) %>%
spread(temp, value)


#   month Amy_A Amy_B Bob_A Bob_B
# 1     1     9     6     8     5
# 2     2     7     7     6     6
# 3     3     6     8     9     7

EDIT 22/10/2019

As mentioned in comments by @gjabel, newer tidyr versions (v1.0.0+) have now pivot_wider and pivot_longer functions (currently in maturing state), hence, a newer approach would be

pivot_wider(data = df,
id_cols = month,
names_from = student,
values_from = c("A", "B"))
# # A tibble: 3 x 5
#     month A_Amy A_Bob B_Amy B_Bob
#     <int> <dbl> <dbl> <dbl> <dbl>
#   1     1     9     8     6     5
#   2     2     7     6     7     6
#   3     3     6     9     8     7

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