Question

我想从data.frame的每一行独立于其他行绘制随机样本。这是一个例子。此代码为每行选择相同的列，但我需要为每行选择独立的列。

library(plyr)
set.seed(12345)
df1 <- mdply(data.frame(mean=c(10, 15)), rnorm, n = 5, sd = 1)
df1
  mean       V1       V2        V3        V4       V5
1   10 10.58553 10.70947  9.890697  9.546503 10.60589
2   15 13.18204 15.63010 14.723816 14.715840 14.08068
> df1[ , -1]
        V1       V2        V3        V4       V5
1 10.58553 10.70947  9.890697  9.546503 10.60589
2 13.18204 15.63010 14.723816 14.715840 14.08068
> sample(df1[, -1], replace = TRUE)
         V3       V2       V5        V4      V4.1
1  9.890697 10.70947 10.60589  9.546503  9.546503
2 14.723816 15.63010 14.08068 14.715840 14.715840
> t(apply(df1[, -1], 1, sample))
         [,1]      [,2]     [,3]     [,4]      [,5]
[1,] 10.70947  9.890697 10.60589 10.58553  9.546503
[2,] 14.71584 13.182044 14.08068 15.63010 14.723816

被修改

df1[ , -1]
            V1       V2        V3        V4       V5
    1 10.58553 10.70947  9.890697  9.546503 10.60589
    2 13.18204 15.63010 14.723816 14.715840 14.08068

sample(df1[, -1], replace = TRUE)
             V3       V2       V5        V4      V4.1
    1  9.890697 10.70947 10.60589  9.546503  9.546503
    2 14.723816 15.63010 14.08068 14.715840 14.715840

sample(df1[, -1], replace = TRUE)为两行选择列V3，V2，V5，V4和V4。但我要求它可以为V3选择列V2，V5，V4，V4和first row和/或任意组合second row的五列。

Answer 1

您可以将apply与replace=TRUE用于sample

 t(apply(df1[,-1], 1, sample, replace=TRUE))

Answer 2

您可以一次性对列索引进行采样，然后使用矩阵子集来避免使用apply：

## Determine how many indices are required (nrow x (ncol - 1))
nsamp <- prod(dim(df1[, -1]))

## Sample from the number of desired columns, here 5 = ncol(df1[, -1])
mySamp <- sample.int(5, nsamp, replace = TRUE)

## Create a matrix of row and column indices
## Have to add 1 to mySamp to ignore first column of df1
myIdx <- cbind(rep(seq_len(nrow(df1)), ncol(df1) - 1), mySamp + 1)

## Return the corresponding values
matrix(df1[myIdx], nrow = nrow(df1))

#           [,1]     [,2]      [,3]      [,4]     [,5]
# [1,]  9.890697 10.60589  9.546503  9.546503 10.70947
# [2,] 15.630099 14.71584 15.630099 14.723816 14.72382

来自data.frame的每列的随机样本

2 个答案: