Data wrangling (1): Conversion of the list and data frame types

Abstract: Conversion of a dataset between the list type and the data frame type.

Convert the data frame to list using the function as.list(). Convert the list to the data frame using do.call().

> #convert data frame into list

> #data frame

> df<-as.data.frame(matrix(1:12, nrow=3))

> df

V1 V2 V3 V4

1 1 4 7 10

2 2 5 8 11

3 3 6 9 12

> #conversion by columns

> my.list<-as.list(df)

> my.list

$V1

[1] 1 2 3

$V2

[1] 4 5 6

$V3

[1] 7 8 9

$V4

[1] 10 11 12

>

> #convert list to data frame

> do.call(cbind, my.list)

V1 V2 V3 V4

[1,] 1 4 7 10

[2,] 2 5 8 11

[3,] 3 6 9 12

The R package plyr provide the function laply() for convert the list with different length to a data frame

> #convert list with different length into data frame

> library(plyr)

> #

> my.list<-list('a'=c(1,3,4), 'b'=c(1,2,6,7))

> my.list

$a

[1] 1 3 4

$b

[1] 1 2 6 7

> my.df<-t(ldply(.data=my.list, .fun=rbind))

> colnames(my.df)<-my.df[1,]

> my.df<-my.df[-1,]

> my.df

a b

1 "1" "1"

2 "3" "2"

3 "4" "6"

4 NA " 7"

Writing date: 20150511