# [R] Question: concatenating lists

Putter, H. (MStat) H.Putter at lumc.nl
Mon Oct 14 17:03:40 CEST 2002

```Dear R users,

I have the following problem. I have a number of lists with identical
structure. Each component is a vector, matrix or array, but components of
different lists may be of different size. How do I combine the lists to get
a new list such that each component of this list contains the components of
the individual lists?

An example may explain most clearly what I need.

Suppose I have three lists:
list1 <- list(a=1:2,b=matrix(1,2,2))
list2 <- list(a=3:5,b=matrix(-1,3,3))
list3 <- list(a=6:9,b=matrix(5,4,4))

The result should give me something like:

\$a:
[,1] [,2] [,3]
[1,]    1    3    6
[2,]    2    4    7
[3,]   NA    5    8
[4,]   NA   NA    9

\$b:
, , 1
[,1] [,2] [,3] [,4]
[1,]    1    1   NA   NA
[2,]    1    1   NA   NA
[3,]   NA   NA   NA   NA
[4,]   NA   NA   NA   NA

, , 2
[,1] [,2] [,3] [,4]
[1,]   -1   -1   -1   NA
[2,]   -1   -1   -1   NA
[3,]   -1   -1   -1   NA
[4,]   NA   NA   NA   NA

, , 3
[,1] [,2] [,3] [,4]
[1,]    5    5    5    5
[2,]    5    5    5    5
[3,]    5    5    5    5
[4,]    5    5    5    5

Any ideas would be much appreciated.
Best regards,
Hein

Hein Putter
Department of Medical Statistics
Leiden University Medical Center
P.O.Box 9604,
2300 RC Leiden, The Netherlands
phone  +31-71-5276827
fax    +31-71-5276799
e-mail h.putter at lumc.nl
http://www.medstat.medfac.leidenuniv.nl/MS/Hp

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```