将列表作为数据框架最有效的方法是什么？ [英] What is the most efficient way to cast a list as a data frame?

问题描述

很多时候，我想转换一个列表，其中每个索引具有相同的元素类型到数据帧。例如，我可能有一个列表：

Very often I want to convert a list wherein each index has identical element types to a data frame. For example, I may have a list:

> my.list
[[1]]
[[1]]$global_stdev_ppb
[1] 24267673

[[1]]$range
[1] 0.03114799

[[1]]$tok
[1] "hello"

[[1]]$global_freq_ppb
[1] 211592.6


[[2]]
[[2]]$global_stdev_ppb
[1] 11561448

[[2]]$range
[1] 0.08870838

[[2]]$tok
[1] "world"

[[2]]$global_freq_ppb
[1] 1002043

我想将此列表转换为数据帧， index元素是一列。自然（对我）的事情是使用 do.call ：

I want to convert this list to a data frame where each index element is a column. The natural (to me) thing to go is to is use do.call:

> my.matrix<-do.call("rbind", my.list)
> my.matrix
     global_stdev_ppb range      tok     global_freq_ppb
[1,] 24267673         0.03114799 "hello" 211592.6       
[2,] 11561448         0.08870838 "world" 1002043

直截了当，但是当我尝试将此矩阵转换为数据帧时，列仍然是列表元素，而不是向量：

Straightforward enough, but when I attempt to cast this matrix as a data frame, the columns remain list elements, rather than vectors:

> my.df<-as.data.frame(my.matrix, stringsAsFactors=FALSE)
> my.df[,1]
[[1]]
[1] 24267673

[[2]]
[1] 11561448

目前，为了正确地获取数据框架，我使用 unlist 和 as.vector ，然后重新创建数据框：

Currently, to get the data frame cast properly I am iterating over each column using unlist and as.vector, then recasting the data frame as such:

new.list<-lapply(1:ncol(my.matrix), function(x) as.vector(unlist(my.matrix[,x])))
my.df<-as.data.frame(do.call(cbind, new.list), stringsAsFactors=FALSE)

但是，似乎效率很低。有没有更好的方法呢？

This, however, seem very inefficient. Is there are better way to do this?

推荐答案

我想你想要的：

> do.call(rbind, lapply(my.list, data.frame, stringsAsFactors=FALSE))
  global_stdev_ppb      range   tok global_freq_ppb
1         24267673 0.03114799 hello        211592.6
2         11561448 0.08870838 world       1002043.0
> str(do.call(rbind, lapply(my.list, data.frame, stringsAsFactors=FALSE)))
'data.frame':   2 obs. of  4 variables:
 $ global_stdev_ppb: num  24267673 11561448
 $ range           : num  0.0311 0.0887
 $ tok             : chr  "hello" "world"
 $ global_freq_ppb : num  211593 1002043

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