在矩阵上使用带有均值函数的mapply [英] Using mapply with mean function on a matrix

问题描述

我希望计算矩阵每一列(或行)中相邻值的平均值(例如[1,1]和[2,1]，[2,1]和[3,1]的平均值， [3,1]和[4,1])，并将其应用于所有列.

I wish to calculate the mean of adjacent values in each column (or row) of a matrix (e.g. mean of [1,1] and [2,1], [2,1] and [3,1], [3,1] and [4,1]) and to apply this across all columns.

我尝试使用mapply函数(避免使用for循环)，计算每列中前两个值的平均值，并计划将其逐行应用于整个矩阵.但是，如果我尝试对值求和而不是对均值函数求和，那么mapply似乎有效.

I have tried to use the mapply function (to avoid using a for loop), to calculate the mean of the first 2 values in each column, and plan to apply this to the whole matrix row-by-row. However mapply which seems to work if I try to sum the values but not for the mean function.

请参见下面的示例:

x <- matrix(c(NA,rnorm(28),NA), nrow=6, ncol=5)
print(x)
       [,1]       [,2]       [,3]       [,4]       [,5]
[1,]          NA -0.6557176  1.7741320  0.3667700 -0.5548408
[2,]  0.14001643  0.2521062 -0.1295084 -0.4272368  0.7598425
[3,]  0.32123196  0.5736409  0.8618268  2.1535191  0.4686728
[4,]  0.06573949 -1.2101965 -0.4308219 -0.2624877 -0.3751350
[5,] -0.66247996  1.2743463  1.6044236  1.2004990 -0.3283678
[6,]  1.05005260  1.2264607  3.2347421 -0.8113528         NA

mapply(sum, x[1,], x[2,])
[1]          NA -0.40361136  1.64462358 -0.06046682  0.20500169
# gives the sum of the input of rows 1 and 2 for each column, as expected

mapply(mean, x[1,], x[2,])
[1]         NA -0.6557176  1.7741320  0.3667700 -0.5548408
# gives the actual values across row 1

使用均值函数时，输出似乎是第一行的值.我怀疑问题出在索引正确的输入值上.

When using the mean function, the output appears to be the values of the first row. I suspect the problem is in indexing the correct input values.

推荐答案

您可以使用:

library(zoo)
apply(x, 2, function(x) rollapply(x, 2, mean))

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