R：根据指定值计算行的差异

Question

我的数据框看起来像这样：

Game Team Value
1      A    0.6
1      B    0.5
2      C    1.2
2      D    0.3

我想创建一个新列来计算＆＃39;值的差异＆＃39;对于给定的游戏，所以它将是：

difference
0.1
-0.1
0.9
-0.9

换句话说，我想通过“游戏”进行分组。但我不太清楚如何做到这一点

Answer 1

使用ave的简单基础R解决方案可能是

with(df, ave(Value, Game, FUN = diff)) * c(-1, 1)
# [1]  0.1 -0.1  0.9 -0.9

Answer 2

如果每组只有两个元素：

library(data.table)

# using @DavidArenburg clean trick
# otherwise c(diff(rev(Value)),diff(Value)) makes it

setDT(df)[,difference:=diff(Value)*c(-1,1), by = Game][]  
   Game Team Value difference
1:    1    A   0.6        0.1
2:    1    B   0.5       -0.1
3:    2    C   1.2        0.9
4:    2    D   0.3       -0.9

Answer 3

您还可以使用aggregate

使用Base R解决方案

c(t(aggregate(Value~Game, df, function(x) c(diff(rev(x)), diff(x)))[, -1]))
[1]  0.1 -0.1  0.9 -0.9

Answer 4

使用dplyr

library(dplyr)
df1 %>% 
    group_by(Game) %>%
    mutate(difference = diff(Value)*c(-1,1))
#   Game  Team Value difference
#  (int) (chr) (dbl)      (dbl)
#1     1     A   0.6        0.1
#2     1     B   0.5       -0.1
#3     2     C   1.2        0.9
#4     2     D   0.3       -0.9