[R] Combine list element by column name to make a dataframe

peter dalgaard pdalgd at gmail.com
Mon Apr 6 10:41:02 CEST 2015


> On 06 Apr 2015, at 08:05 , Mohammad Tanvir Ahamed via R-help <r-help at r-project.org> wrote:
> 
> Hi ,�
> 
> I have a example list like follow�
> 
> 
> ############################################
> 
> lst<-list(setNames(c(1,10,50,60,70,80),c("id","id1","math","phy","che","bio")),setNames(c(2,20,45),c("id","id1","phy")),setNames(c(3,30,75),c("id","id1","bio")))
> 
> 
> My expected outcome :�
> 
> ---------------------------------------------------------------------
> 
> df<-rbind(c(1,10,50,60,70,80),c(2,20,NA,45,NA,NA),c(3,30,NA,NA,NA,75))
> 
> colnames(df)<-c("id","id1","math","phy","che","bio")
> 
> row.names(df) <- NULL
> 
> df
> 
> ############################################
> 
> 
> Any suggestion will be appreciated .�

Hmm, in principle this looks like a merge() problem, if you first convert each list element to a data frame. That could be painful to get right though.

You could try something like this:

> nm <- Reduce(union, lapply(lst, names)) # or just type it in
> nm
[1] "id"   "id1"  "math" "phy"  "che"  "bio" 
> blank <- setNames(rep(NA_real_, length(nm)), nm)
> fill1 <- function(x, blank) {blank[names(x)] <- x; blank}
> lapply(lst, fill1, blank)
[[1]]
  id  id1 math  phy  che  bio 
   1   10   50   60   70   80 

[[2]]
  id  id1 math  phy  che  bio 
   2   20   NA   45   NA   NA 

[[3]]
  id  id1 math  phy  che  bio 
   3   30   NA   NA   NA   75 

> do.call(rbind,lapply(lst, fill1, blank))
     id id1 math phy che bio
[1,]  1  10   50  60  70  80
[2,]  2  20   NA  45  NA  NA
[3,]  3  30   NA  NA  NA  75

(NB, this is a matrix, not a data frame, but so is your "df"!)

Notice that this does not do a proper merge on the id fields, i.e. if you have two different records with different grades (say one with "che" and another with "phy") on the same id, you get two records, not one. However, that might well be what you wanted.

(It is tempting to use 

> fill1 <- function(x) `[<-`(blank, names(x), x)
> lapply(lst, fill1)

which does seem to work, but should probably be avoided because of the risk of destructive modification.) 


> 
> Thanks in advance.
> 
>> 
> Best regards
> 
> 
> ...........................�
> 
> Tanvir Ahamed
> 
> G�teborg, Sweden
> 
> 
> 
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com



More information about the R-help mailing list