计算R中的多个字符串，按这些字符串分组答案

【问题标题】：count multiple strings in R, group by those strings计算R中的多个字符串，按这些字符串分组
【发布时间】：2017-11-13 05:34:43
【问题描述】：

我有一个这样的data.frame：

Points      Assists      Steals
Player A    Player B     Player B
Player B    Player C     Player A
player C    Player C     Player A

我正在尝试获得这样的 data.frame 输出：

           Points     Assists      Steals
Player A    1          0            2
Player B    1          1            1
Player C    1          2            0

如您所见，我希望它计算每个玩家出现在每个类别中的次数。我可以使用table() 为一列执行此操作，但不知道如何为多列执行此操作。我该怎么做？

【问题讨论】：

标签： r

【解决方案1】：

我们可以将gather 转换为长格式，将count 和spread 转换为宽格式

library(dplyr)
library(tidyr)
gather(df1) %>% 
     count(key, value) %>%
     spread(key, n, fill = 0)
# A tibble: 3 x 4
#     value Assists Points Steals
#*    <chr>   <dbl>  <dbl>  <dbl>
#1 Player A       0      1      2
#2 Player B       1      1      1
#3 Player C       2      1      0

或者我们使用melt 和table

library(reshape2)
table(melt(as.matrix(df1))[3:2])
#         Var2
#value      Points Assists Steals
#  Player A      1       0      2
#  Player B      1       1      1
#  Player C      1       2      0

数据

df1 <- structure(list(Points = c("Player A", "Player B", "Player C"), 
Assists = c("Player B", "Player C", "Player C"), Steals = c("Player B", 
"Player A", "Player A")), .Names = c("Points", "Assists", 
"Steals"), class = "data.frame", row.names = c(NA, -3L))

【讨论】：

是否有 data.table 方法可以做到这一点？我不确定我会怎么做。我喜欢桌子融化的方式，简单而聪明
@denis 谢谢。你可以做dcast(melt(setDT(df1, keep.rownames = TRUE)[], id.var = 'rn'), value ~variable)

【解决方案2】：

这里是 data.table 包的 akrun 解决方案的详细信息。可能只有一行，但我将其扩展为几个可以理解的步骤。

library(data.table)
DT <- setDT(df1)
DT[,id := 1:.N]
plouf <- melt(DT, id.var = c("id"))
dcast(plouf, value ~variable)

给予

      value Points Assists Steals
1: Player A      1       0      2
2: Player B      1       1      1
3: Player C      1       2      0

【讨论】：