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I am wondering how I can convert a list with both numeric and string variables to a dataframe:

For example:

aa<-c("a","b","b","b","d")
bb<-c("Yes","No","No","Yes","Yes")
cc<-c(1,2,4,4,3)

x<-list(aa=aa,bb=bb,cc=cc)

How can I convert x to a dataframe, such that when I call x I get:

  aa  bb cc
1  a Yes  1
2  b  No  2
3  b  No  4
4  b Yes  4
5  d Yes  3

Thanks!

Head and toes
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4 Answers4

3

With large data in a list, it's recommended to change the data "in place".

For reference, see Simon Urbanek's answer here: Quickly reading very large tables as dataframes in R

attr(x, "row.names") <- .set_row_names(unique(lengths(x)))
class(x) <- "data.frame"
x
#   aa  bb cc
# 1  a Yes  1
# 2  b  No  2
# 3  b  No  4
# 4  b Yes  4
# 5  d Yes  3

This has two major advantages over as.data.frame One is that it avoids copying the object x. The other is that it keeps the column classes in line with the list classes (see the following). With as.data.frame, character classes would be converted to factors.

sapply(x, class)
#          aa          bb          cc 
# "character" "character"   "numeric"
Community
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Rich Scriven
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1

A data.table would also have a class of data.frame, so you can make use of the efficient setDT function:

x <- list(aa = aa, bb = bb, cc = cc)

library(data.table)
setDT(x)
is.data.frame(x)
# [1] TRUE
str(x)
# Classes ‘data.table’ and 'data.frame':    5 obs. of  3 variables:
#  $ aa: chr  "a" "b" "b" "b" ...
#  $ bb: chr  "Yes" "No" "No" "Yes" ...
#  $ cc: num  1 2 4 4 3
#  - attr(*, ".internal.selfref")=<externalptr>
A5C1D2H2I1M1N2O1R2T1
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0

You can do x<-as.data.frame(x).

Updated based on @Frank's good below, if you want to avoid converting characters to factors do

x<-as.data.frame(x, StringsAsFactors = FALSE).

Elin
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    Just a note about column classes. The above solution will convert the character vectors to factor, by default. A way to prevent this, is to use `stringsAsFactors = FALSE` like so `data.frame(x, stringsAsFactors = FALSE)`. – Jota Aug 24 '14 at 15:07
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> x = data.frame(aa,bb,cc)
> x
  aa  bb cc
1  a Yes  1
2  b  No  2
3  b  No  4
4  b Yes  4
5  d Yes  3
> 
> str(x)
'data.frame':   5 obs. of  3 variables:
 $ aa: Factor w/ 3 levels "a","b","d": 1 2 2 2 3
 $ bb: Factor w/ 2 levels "No","Yes": 2 1 1 2 2
 $ cc: num  1 2 4 4 3
>

or:

> x = data.frame(aa,bb,cc, stringsAsFactors=F)
> x
  aa  bb cc
1  a Yes  1
2  b  No  2
3  b  No  4
4  b Yes  4
5  d Yes  3
> str(x)
'data.frame':   5 obs. of  3 variables:
 $ aa: chr  "a" "b" "b" "b" ...
 $ bb: chr  "Yes" "No" "No" "Yes" ...
 $ cc: num  1 2 4 4 3
>
rnso
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