# [R] listing a sequence of vectors in a matrix

Robin Hankin r.hankin at noc.soton.ac.uk
Tue Aug 22 15:05:06 CEST 2006

```Gabor makes a good point about seq() vs a:b [a common gotcha
for me].

I'll revise my original function to:

> f <- function(a,n){(seq(length=a))[1:n]}
> t(sapply(c(2,3,4,4,4,5,6,0),f,n=5))
[,1] [,2] [,3] [,4] [,5]
[1,]    1    2   NA   NA   NA
[2,]    1    2    3   NA   NA
[3,]    1    2    3    4   NA
[4,]    1    2    3    4   NA
[5,]    1    2    3    4   NA
[6,]    1    2    3    4    5
[7,]    1    2    3    4    5
[8,]   NA   NA   NA   NA   NA
>

rksh

On 22 Aug 2006, at 13:55, Gabor Grothendieck wrote:

> Here are two solutions.  seq(length = ...) instead of
> just seq(...) is so that v can possibly contain zeros.
>
> # data
> v <- 3:5
>
> # solution 1 - rbind/lapply
> f <- function(n) {
> 	s = seq(length = n)
> 	replace(rep(NA, max(v)), s, s)
> }
> do.call(rbind, lapply(v, f))
>
> # solution 2 - loop
> mat <- matrix(NA, length(v), max(v))
> for(i in seq(v)) {
> 	s <- seq(length = v[i])
> 	mat[i, s] <- s
> }
>
>
> On 8/22/06, Sara-Jane Dunn <SND at bas.ac.uk> wrote:
>> Hi,
>>
>> I'm having trouble applying the matrix function. I'd like to be
>> able to
>> create a matrix of vectors filled in by rows, which are not all
>> the same
>> length, and so I need it to fill in NAs where applicable.
>>
>> It's easiest to explain with a simple example:
>>
>> Suppose vec = c(3,4,5). How can I form a matrix of the vectors
>> 1:vec[j]
>> for j=1:3?
>> i.e. 1   2   3   NA NA
>>      1   2   3   4   NA
>>      1   2   3   4    5
>> I've tried matrix(c(1:vec[j]),nrow=max(j),ncol=max(vec)) but it will
>> only give me a matrix with repeated values for j=1, like   1  2  3  1
>> 2
>>                                            3  1  2  3  1
>>                                            2  3  1  2  3
>>
>> Also using the list function hasn't got me anywhere either..
>>
>> Any help/ideas would be greatly appreciated!
>>
>> Many thanks,
>> Sara-Jane Dunn
>>
>> --
>> This message (and any attachments) is for the recipient only...
>> {{dropped}}
>>
>> ______________________________________________
>> R-help at stat.math.ethz.ch mailing list
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>> guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> guide.html
> and provide commented, minimal, self-contained, reproducible code.

--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
tel  023-8059-7743

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