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

[peter dalgaard]

> 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]]
> 
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-- 
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