Convert list with NULL entres to data.frame in R

Question

I have a list named z :

z<-list( list(a=1, b=2),  list(a=2, b=3), list(a=NULL, b=4))

I want this to be converted to a data.frame with the corresponding a entry in the data.frame assigned as NULL. Doing this,

do.call( rbind, lapply( z, data.frame, stringsAsFactors=TRUE ) )

as expected, gives this error:

 Error in data.frame(a = NULL, b = 4, check.names = FALSE, stringsAsFactors = TRUE) : 
 arguments imply differing number of rows: 0, 1

What is the work around?

What exactly is a NULL value in your data? You sure you're not looking for NA? — A5C1D2H2I1M1N2O1R2T1
– A5C1D2H2I1M1N2O1R2T1, Commented Jun 30, 2013 at 8:45
Yes, I realize it would make equal sense to replace NULL with NA. 'NULL' values are those that are present in a SQL table entry. — Enigman
– Enigman, Commented Jun 30, 2013 at 16:27
@Enigman, probably you should accept the answer (since it's working) and mark this closed. — Arun
– Arun, Commented Jul 5, 2013 at 5:38

A5C1D2H2I1M1N2O1R2T1 · Accepted Answer · 2013-06-30 07:17:52Z

5

Is this what you are trying to do?

> data.frame(do.call(rbind, z))
     a b
1    1 2
2    2 3
3 NULL 4

answered Jun 30, 2013 at 7:17

A5C1D2H2I1M1N2O1R2T1

194k31 gold badges417 silver badges497 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

A5C1D2H2I1M1N2O1R2T1 Over a year ago

@Enigman, right--it appears not. If you view the str of the object created with this answer, both a and b are lists.

Colombo Over a year ago

Not gonna lie, data.frame of lists (list of lists) is super interesting data structure. If you do it with a named list of lists that are themselves named, you will be able to do df$column$row. And then assign whatever to this.

user1609452 · Accepted Answer · 2013-06-30 07:18:54Z

2

 as.data.frame(do.call(rbind, z))
     a b
1    1 2
2    2 3
3 NULL 4

answered Jun 30, 2013 at 7:18

user1609452

4,4641 gold badge17 silver badges20 bronze badges

Comments

Ricky · Accepted Answer · 2015-06-09 02:45:10Z

2

If you're interested in data frame of numeric values instead of data frame of lists, you can try the below.

lz <- lapply(z, function(x) {
    nonnull <- sapply(x, typeof)!="NULL"
    do.call(data.frame, c(x[nonnull], stringsAsFactors=FALSE))
})

require(plyr)
df <- ldply(lz)

Note that the result will have NULLs converted to NAs to form valid dataframes.

> df
   a b
1  1 2
2  2 3
3 NA 4
> str(df)
'data.frame':   3 obs. of  2 variables:
 $ a: num  1 2 NA
 $ b: num  2 3 4

answered Jun 9, 2015 at 2:45

Ricky

4,7166 gold badges45 silver badges73 bronze badges

Collectives™ on Stack Overflow

Convert list with NULL entres to data.frame in R

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related