需要利用R的回收一次

Question

我想根据第一列对列 df$candidate1 到 df$candidate5 中的单元格进行索引。

在某些情况下，候选人是空的，在这种情况下我想循环回到第一个候选人。例如，我可以让 df$old=4 和 df$candidate1=0.47 以及 df$candidate2=-0.14 和 candidates 3/4/5 全部空白。在那种情况下，我想检索 candidate2（因为它搜索向量 c(0.47,-0.14,0.47,-0.14) 并检索第四个元素。

  old candidate1 candidate2 candidate3 candidate4 candidate5   new
1   4       0.47      -0.14         NA         NA         NA -0.14

下面是一个可重现的示例虚拟数据和一个不回收的for循环（但显示了过程的基础知识).

问：如何进行回收？

set.seed(123)
size <- 10
df <- data.frame(old = sample(1:5, size, replace = TRUE), 
                 candidate1 = rnorm(size),
                 candidate2 = rnorm(size),
                 candidate3 = rnorm(size),
                 candidate4 = rnorm(size),
                 candidate5 = rnorm(size))
df$candidate5 <- ifelse(runif(size, 0, 1) < 0.5, NA, df$candidate5) # sometimes this (and other) columns are empty, I want to recycle over at candidate1

# this for loop works but it doesn't recycle
new <- vector(mode = "numeric", length = size)
for (i in 1:size){
  new[i] <- df[i,1+df$old[i]]
}
df$new <- new
df$new[6] <- df$candidate1[6] # filling in the missed cell because my for loop doesn't recycle, value = 0.11068272

# conceptually, below is what I tried first, but this pulls a full vector for each row (and will overload R, so test with caution!)
df$new <- df[,2:6][df$old]

上述可重现示例的输出

# df[6,7] (0.11068272) was filled in manually to show the desired output

   old candidate1 candidate2  candidate3 candidate4  candidate5         new
1    3 -0.6868529  0.7013559 -1.13813694 -0.3059627  0.77996512 -1.13813694
2    3 -0.4456620 -0.4727914  1.25381492 -0.3804710 -0.08336907  1.25381492
3    2  1.2240818 -1.0678237  0.42646422 -0.6947070  0.25331851 -1.06782371
4    2  0.3598138 -0.2179749 -0.29507148 -0.2079173          NA -0.21797491
5    3  0.4007715 -1.0260044  0.89512566 -1.2653964 -0.04287046  0.89512566
6    5  0.1106827 -0.7288912  0.87813349  2.1689560          NA  0.11068272
7    4 -0.5558411 -0.6250393  0.82158108  1.2079620          NA  1.20796200
8    1  1.7869131 -1.6866933  0.68864025 -1.1231086          NA  1.78691314
9    2  0.4978505  0.8377870  0.55391765 -0.4028848          NA  0.83778704
10   3 -1.9666172  0.1533731 -0.06191171 -0.4666554  0.58461375 -0.06191171

Answer 1

我认为这行得通。我将候选列提取到矩阵中，回收它们，然后使用该回收对象创建 new 列：

m_recycle = as.matrix(df[, 2:6])
m_recycle = t(apply(m_recycle, 1, function(x) rep(x[!is.na(x)], length.out = 5)))

df$new = m_recycle[cbind(1:nrow(m_recycle), df$old)]
df
#    old candidate1 candidate2 candidate3  candidate4  candidate5         new
# 1    2  1.7150650  1.7869131 -1.6866933  0.68864025 -1.12310858  1.78691314
# 2    4  0.4609162  0.4978505  0.8377870  0.55391765          NA  0.55391765
# 3    3 -1.2650612 -1.9666172  0.1533731 -0.06191171          NA  0.15337312
# 4    5 -0.6868529  0.7013559 -1.1381369 -0.30596266  0.77996512  0.77996512
# 5    5 -0.4456620 -0.4727914  1.2538149 -0.38047100 -0.08336907 -0.08336907
# 6    1  1.2240818 -1.0678237  0.4264642 -0.69470698          NA  1.22408180
# 7    3  0.3598138 -0.2179749 -0.2950715 -0.20791728 -0.02854676 -0.29507148
# 8    5  0.4007715 -1.0260044  0.8951257 -1.26539635 -0.04287046 -0.04287046
# 9    3  0.1106827 -0.7288912  0.8781335  2.16895597  1.36860228  0.87813349
# 10   3 -0.5558411 -0.6250393  0.8215811  1.20796200          NA  0.82158108

不过，我的数据与你的不匹配。也许你没有运行 set.seed?

需要利用R的回收一次

Need to take advantage of R's recycling for once

indexing

r

recycle