Question

经验丰富的R用户，

这有点简单。我想根据一个可控变量将x加Group.1。

当我说出类似的内容时，我想通过对前两行进行分组来总结x：number <- 2 如果我说3，则应将前三行的x加Group.1

知道如何解决这个问题吗？我应该写一个函数吗？非常感谢你们。

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

Answer 1

假设您的数据位于mydata：

with(mydata, sum(x[Group.1 <= 2])

Answer 2

如果你想要的总和总是累积的，那么就有一个函数，cumsum。它的工作原理如下。

> cumsum(c(1,2,3))
[1] 1 3 6

在这种情况下，您可能需要类似

的内容

> mysum <- cumsum(yourdata$x)
> mysum[2] # the sum of the first two rows
> mysum[3] # the sum of the first three rows
> mysum[number] # the sum of the first "number" rows

Answer 3

您可以使用by功能。

例如，给定以下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

Answer 4

不确定为什么Eggs在这里很重要;）

df1 <- data.frame(Gr=seq(4),
                  x=c(230299, 263066, 266504, 177196)
                  )

现在使用n=2，即前两行：

n <- 2
sum(df1[, "x"][df1[, "Gr"]<=n])

表达式[df1[, "Gr"]<=n]创建一个逻辑向量，以便在df1[, "x"]之前对sum中的元素进行子集化。

此外，您的Group.1似乎与行号相同。如果是这样，这可能会更简单：

sum(df1[, "x"][1:n])

或立刻获得所有

cumsum(df1[, "x"])

Answer 5

如果您只想对数据的一部分求和：

my_data <- data.frame(c("TRUE","FALSE","FALSE","FALSE","TRUE"), c(1,2,3,4,5))
names(my_data)[1] <- "DESCRIPTION" #Change Column Name
names(my_data)[2] <- "NUMBER"      #Change Column Name

sum(subset(my_data, my_data$DESCRIPTION=="TRUE")$NUMBER)

您应该得到6。

在R中，如何用某种逻辑对数据帧的某些行求和？

5 个答案: