如何获得所选列的平均值(平均值) [英] How can I get the average (mean) of selected columns

问题描述

我想获得每行某些列的平均值.

I would like to get the average for certain columns for each row.

我有这个数据:

w=c(5,6,7,8)
x=c(1,2,3,4)
y=c(1,2,3)
length(y)=4
z=data.frame(w,x,y)

哪个返回:

  w x  y
1 5 1  1
2 6 2  2
3 7 3  3
4 8 4 NA

我想获得某些列的平均值，而不是所有列的平均值.我的问题是我的数据中有很多 NA.所以如果我想要 x 和 y 的平均值，这就是我想要的:

I would like to get the mean for certain columns, not all of them. My problem is that there are a lot of NAs in my data. So if I wanted the mean of x and y, this is what I would like to get back:

  w x  y mean
1 5 1  1    1
2 6 2  2    2
3 7 3  3    3
4 8 4 NA    4

我想我可以做类似 z$mean=(z$x+z$y)/2 的事情，但是 y 的最后一行是 NA，所以显然我不希望 NA 是计算出来的，我不应该除以二.我尝试了 cumsum 但是当该行中有一个 NA 时它会返回 NA.我想我正在寻找可以添加所选列的东西，忽略 NA，获取没有 NA 的所选列的数量并除以该数字.我试过 ??mean 和 ??average 并且完全被难住了.

I guess I could do something like z$mean=(z$x+z$y)/2 but the last row for y is NA so obviously I do not want the NA to be calculated and I should not be dividing by two. I tried cumsum but that returns NAs when there is a single NA in that row. I guess I am looking for something that will add the selected columns, ignore the NAs, get the number of selected columns that do not have NAs and divide by that number. I tried ??mean and ??average and am completely stumped.

ETA:是否还有一种方法可以为特定列添加权重?

ETA: Is there also a way I can add a weight to a specific column?

推荐答案

以下是一些示例:

> z$mean <- rowMeans(subset(z, select = c(x, y)), na.rm = TRUE)
> z
  w x  y mean
1 5 1  1    1
2 6 2  2    2
3 7 3  3    3
4 8 4 NA    4

加权平均

> z$y <- rev(z$y)
> z
  w x  y mean
1 5 1 NA    1
2 6 2  3    2
3 7 3  2    3
4 8 4  1    4
> 
> weight <- c(1, 2) # x * 1/3 + y * 2/3
> z$wmean <- apply(subset(z, select = c(x, y)), 1, function(d) weighted.mean(d, weight, na.rm = TRUE))
> z
  w x  y mean    wmean
1 5 1 NA    1 1.000000
2 6 2  3    2 2.666667
3 7 3  2    3 2.333333
4 8 4  1    4 2.000000

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