将函数应用于 R 中 data.frame 中的组 [英] Apply a function to groups within a data.frame in R
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问题描述
我正在尝试获取数据框中组(a"和b")的变量 (v) 的累积总和.如何将底部的结果(其行的偶数编号正确)放入数据框的 cs 列中?
I am trying to get the cumulative sum of a variable (v) for groups ("a" and "b") within a dataframe. How can I get the result at the bottom -- whose rows are even numbered properly -- into column cs of my dataframe?
> library(nlme)
> g <- factor(c("a","b","a","b","a","b","a","b","a","b","a","b"))
> v <- c(1,4,1,4,1,4,2,8,2,8,2,8)
> cs <- rep(0,12)
> d <- data.frame(g,v,cs)
> d
g v cs
1 a 1 0
2 b 4 0
3 a 1 0
4 b 4 0
5 a 1 0
6 b 4 0
7 a 2 0
8 b 8 0
9 a 2 0
10 b 8 0
11 a 2 0
12 b 8 0
> r=gapply(d,FUN="cumsum",form=~g, which="v")
>r
$a
v
1 1
3 2
5 3
7 5
9 7
11 9
$b
v
2 4
4 8
6 12
8 20
10 28
12 36
> str(r)
List of 2
$ a:'data.frame': 6 obs. of 1 variable:
..$ v: num [1:6] 1 2 3 5 7 9
$ b:'data.frame': 6 obs. of 1 variable:
..$ v: num [1:6] 4 8 12 20 28 36
我想我可以想出一些费力的方法来将这些数据帧中的数据导入 d$cs,但是我缺少一些简单的调整.
I guess I could figure out some laborious way to get the data from those dataframes into d$cs, but there's got to be some easy tweak I'm missing.
推荐答案
我会使用 ave
.如果您查看 ave
的源代码,您会发现它基本上包含了 Martin Morgan 的解决方案.
I would use ave
. If you look at the source of ave
, you'll see it essentially wraps Martin Morgan's solution.
R> g <- factor(c("a","b","a","b","a","b","a","b","a","b","a","b"))
R> v <- c(1,4,1,4,1,4,2,8,2,8,2,8)
R> d <- data.frame(g,v)
R> d$cs <- ave(v, g, FUN=cumsum)
R> d
g v cs
1 a 1 1
2 b 4 4
3 a 1 2
4 b 4 8
5 a 1 3
6 b 4 12
7 a 2 5
8 b 8 20
9 a 2 7
10 b 8 28
11 a 2 9
12 b 8 36
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