在 R 中，如何将数据帧的某些行与某些逻辑相加? [英] In R, how to sum certain rows of a data frame with certain logic?

问题描述

您好有经验的 R 用户，

Hi experienced R users,

这是一件很简单的事情.我想根据一个可控变量对 x 和 Group.1 求和.

It's kind of a simple thing. I want to sum x by Group.1 depending on one controllable variable.

当我说以下内容时，我想通过对前两行进行分组来对 x 求和:number <- 2如果我说 3，它应该将前三行的 x 与 Group.1

I'd like to sum x by grouping the first two rows when I say something like: number <- 2 If I say 3, it should sum x of the first three rows by Group.1

知道如何解决这个问题吗?我应该写一个函数吗?提前谢谢大家.

Any idea how I might tackle this problem? Should I write a function? Thank y'all in advance.

  Group.1  Group.2      x
1       1     Eggs 230299
2       2     Eggs 263066
3       3     Eggs 266504
4       4     Eggs 177196

推荐答案

您可以使用 by 函数.

例如，给定以下 data.frame:

For instance, given the following data.frame:

d <- data.frame(Group.1=c(1,1,2,1,3,3,1,3),Group.2=c('Eggs'),x=1:8)

> d
  Group.1 Group.2 x
1       1    Eggs 1
2       1    Eggs 2
3       2    Eggs 3
4       1    Eggs 4
5       3    Eggs 5
6       3    Eggs 6
7       1    Eggs 7
8       3    Eggs 8

你可以这样做:

num <- 3 # sum only the first 3 rows

# The aggregation function:
# it is called for each group receiving the 
# data.frame subset as input and returns the aggregated row
innerFunc <- function(subDf){
  # we create the aggregated row by taking the first row of the subset
  row <- head(subDf,1)
  # we set the x column in the result row to the sum of the first "num"
  # elements of the subset
  row$x <- sum(head(subDf$x,num))
  return(row)
}
# Here we call the "by" function:
# it returns an object of class "by" that is a list of the resulting
# aggregated rows; we want to convert it to a data.frame, so we call
# rbind repeatedly by using "do.call(rbind, ... )"
d2 <- do.call(rbind,by(data=d,INDICES=d$Group.1,FUN=innerFunc))

> d2
  Group.1 Group.2  x
1       1    Eggs  7
2       2    Eggs  3
3       3    Eggs 19

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