R:对组应用函数 [英] R: applying a function over a group

问题描述

我希望将函数应用于数据框，然后将该函数的结果存储在数据框的新列中.

I am looking to apply a function to a data frame and then store the results of that function in a new column in the data frame.

这是我的数据框tradeData的示例:

Here is a sample of my data frame, tradeData:

Login   AL  Diff
    a   1   0
    a   1   0
    a   1   0
    a   0   1
    a   0   0
    a   0   0
    a   0   0
    a   1   -1
    a   1   0
    a   0   1
    a   1   -1
    a   1   0
    a   0   1
    b   1   0
    b   0   1
    b   0   0
    b   0   0
    b   1   -1
    c   1   0
    c   1   0
    c   0   1
    c   0   0
    c   1   -1

其中差异"列是我要添加的列.它只是 tradeData 的 row(x-1) 和 row(x) 值之间的差异，按登录分组.

Where the "Diff" column is the column I am trying to add. It just just the difference between the values row(x-1) and row(x) of tradeData, grouped by Login.

以下是我尝试过的一些示例:

Here are some samples of what I've tried:

tradeData$Diff = ave(tradeData$AL,tradeData$Login,FUN = function(x) {diff(x)}) 

和

tradeData$Diff = as.data.frame(with(tradeData,tapply(AL,Login,FUN = diff)))

到目前为止，我发现以下问题很有用:R 将函数应用于数据框的子集，但我不确定如何从这里开始，因为我不断收到错误.

I've found the following question useful thus far: R applying a function to a subset of a data frame but I am unsure how to proceed from here, as I keep getting errors.

谢谢

推荐答案

你可以试试

 with(tradeData, ave(AL, Login, FUN=function(x) -1*c(0, diff(x))))
 #[1]  0  0  0  1  0  0  0 -1  0  1 -1  0  1  0  1  0  0 -1  0  0  1  0 -1

或者使用 data.table 的选项.使用 setDT 将data.frame"转换为data.table".按组计算当前值和下一个值之间的差异(by=Login).shift 函数(在新的 devel 版本中引入)type 等于lead"获取下一个值.

Or an option using data.table. Convert the "data.frame" to "data.table" with setDT. Take the difference between current and next value by group (by=Login). The shift function (introduced in the new devel version) with type equals "lead" gets the next value.

 library(data.table)#data.table_1.9.5 
 setDT(tradeData)[, Diff:=AL-shift(AL, type='lead', 
                          fill=0) , by=Login][]

这篇关于R:对组应用函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！