用该列的中位数替换矩阵的每一列中的NA [英] Replacing NA's in each column of matrix with the median of that column

问题描述

我试图用该列的中位数替换矩阵每一列中的NA，但是当我尝试使用lapply或sapply时出现错误；当我使用for循环并且一次更改一列时，代码起作用了，我在做什么错了?

I am trying to replace the NA's in each column of a matrix with the median of of that column, however when I try to use lapply or sapply I get an error; the code works when I use a for-loop and when I change one column at a time, what am I doing wrong?

示例:

set.seed(1928)
mat <- matrix(rnorm(100*110), ncol = 110)
mat[sample(1:length(mat), 700, replace = FALSE)] <- NA
mat1 <- mat2 <- mat

mat1 <- lapply(mat1,
  function(n) {
     mat1[is.na(mat1[,n]),n] <- median(mat1[,n], na.rm = TRUE)
  }
)   

for (n in 1:ncol(mat2)) {
  mat2[is.na(mat2[,n]),n] <- median(mat2[,n], na.rm = TRUE)
}

推荐答案

我建议使用matrixStats软件包对此向量进行矢量化，而不是使用任一循环来计算每列的中位数(sapply也是感觉到它在每次迭代中都会评估一个函数).

I would suggest vectorizing this using the matrixStats package instead of calculating a median per column using either of the loops (sapply is also a loop in a sense that its evaluates a function in each iteration).

首先，我们将创建一个NA s索引

First, we will create a NAs index

indx <- which(is.na(mat), arr.ind = TRUE)

然后，使用预先计算的列中位数并根据索引替换NA

Then, replace the NAs using the precalculated column medians and according to the index

mat[indx] <- matrixStats::colMedians(mat, na.rm = TRUE)[indx[, 2]]

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