提取data.frame列表的名称以及R中data.frame中的值 [英] Extracting the names of a list of data.frames along with values in the data.frame in R

问题描述

在下面的代码中，j是data.frames的命名列表.我想知道是否有办法:

In below code, j is a named list of data.frames. I was wondering if there might be a way to:

(a)提取data.frame内部变量的数值(即one.short和one.long)，并附加其相关名称(即"AAA"或或"CCC")提取的值?

(a) extract the numeric values of the variables (i.e., one.short and one.long) inside the data.frames and attach their related names (i.e., "AAA" or "BBB" or "CCC") to the extracted values?

(b)如果变量(即one.short或one.long)是NA，那么在提取该变量时将该data.frame的名称更改为NA吗?

(b) if a variable (i.e., one.short or one.long) is NA, then change the name of that data.frame to NA when extracting that variable?

预期输出:

在下面的示例中，我希望我的输出像这样:

In the below example, I expect my output to be like:

one.short = list(c("AAA", .6), c(NA, NA), c("CCC", .4))

one.long = list(c("AAA", .8), c(NA, NA), c(NA, NA))

R代码和可复制的数据:

j <- list(data.frame(one.short = .6, one.long = .8), data.frame(one.short = NA, 
one.long = NA), data.frame(one.short = .4, one.long = NA))

names(j) <- c("AAA", "BBB", "CCC")

# I tried this without success:
one.short = sapply(1:length(j), function(i) j[[i]]$one.short)
one.long  = sapply(1:length(j), function(i) j[[i]]$one.long)

推荐答案

我们可以使用[[来执行此操作而无需匿名功能

We can use the [[ to do this without anonymous function

v1 <- sapply(j, `[[`, 'one.short')
v1
#  AAA BBB CCC 
# 0.6  NA 0.4 

如果我们要设置NA值的名称

If we want to set the names of values that NA

names(v1)[is.na(v1)] <- "NULL"
v1
#   AAA NULL  CCC 
#  0.6   NA  0.4 

---

请注意，NULL需要放在list中，因为它会掉入vector

---

Note that NULLwould need to be in a list because it gets dropped in a vector

c('a', 'b', NULL)
#[1] "a" "b"   


list('a', 'b', NULL)
#[[1]]
#[1] "a"

#[[2]]
#[1] "b"

#[[3]]
#NULL

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