将字符串列表转换为R中的数字数据框 [英] Converting a list of lists of strings to a data frame of numbers in R

问题描述

我有一个字符串列表，如下所示:

I have a list of lists of strings as follows:

> ll

[[1]]
[1] "2" "1"

[[2]]
character(0)

[[3]]
[1] "1"

[[4]]
[1] "1" "8"

最长的列表的长度为2，我想从该列表中构建一个包含2列的数据框.积分还可以将列表中的每个项目转换为数字(或字符(0)不适用).我已经尝试过使用mapply()和data.frame转换为数据框，并用NA填充，如下所示.

The longest list is of length 2, and I want to build a data frame with 2 columns from this list. Bonus points for also converting each item in the list to a number or NA for character(0). I have tried using mapply() and data.frame to convert to a data frame and fill with NA's as follows.

#  Find length of each list element
len = sapply(awards2, length)

#  Number of NAs to fill for column shorter than longest
len = 2 - len

df = data.frame(mapply( function(x,y) c( x , rep( NA , y ) ) , ll , len))

但是，我没有使用上面的代码获得包含 2 列(并且 NA 作为填充符)的数据框.

However, I do not get a data frame with 2 columns (and NA's as fillers) using the code above.

感谢您的帮助.

推荐答案

我们可以使用 stringi 中的 stri_list2matrix .由于 list 元素都是 character 向量，因此可以使用此功能

We can use stri_list2matrix from stringi. As the list elements are all character vectors, it seems okay to use this function

library(stringi)
t(stri_list2matrix(ll))
#     [,1] [,2]
#[1,] "2"  "1" 
#[2,] NA   NA  
#[3,] "1"  NA  
#[4,] "1"  "8" 

如果我们需要转换为 data.frame ，请用 as.data.frame

If we need to convert to data.frame, wrap it with as.data.frame

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