# [R] writing a loop using several list()-objects

travellina tamara.rathcke at glasgow.ac.uk
Tue Sep 13 16:26:01 CEST 2011

```Hi there,

I am looking for some help with a loop which uses three list()-objects:
"sequence" has got numbers, "start" and "end" have got the begin/end time
points which should be applied to the numbers in "sequence". length() of all
three objects is identical, length() of vectors stored in "sequence" is
longer than length() of "start" and "end" whose length() is identical. Here
is an example:

> sequence[2]
[[1]]
[1] 168.848 188.440  87.291 111.333 159.921  76.987  65.633 293.320 440.708

> start[2]
[[1]]
[1] 2 5 8

> end[2]
[[1]]
[1] 4 7 9

I want to calculate sums of numbers in all start:end positions and list the
output again, e.g. I can calculate the sum of the numbers occurring
positions 2 till 4 of "sequence", i.e. between start[[2]][1] and end[[2]][1]
using this code:

sum(unlist(sequence[[2]])[unlist(Sfoot[[2]])[1]:unlist(end[[2]])[1]])

This code works perfectly fine but stops doing so if I put it into a loop:

sums <- list()
for(i in 1:length(start)) { for(j in 1:length(unlist(start[[i]]))) {
sums[[i]][j] <-
list(sum(unlist(sequence[[i]])[unlist(start[[i]])[j]:unlist(end[[i]])[j]]))
}}

The output looks like this:
> durF[[2]]
[[1]]
[1] 387.064

[[2]]
[1] 302.541

[[3]]
[1] 734.028

> durF[[2]]
[[1]]
[1] 387.064  302.541  734.028

Something seems to be wrong with the indexing but no idea how to fix it. I
am not ambitious about creating elegant loops, they simply should work - so
please do not hesitate to make any suggestion: clunky or not, it will be
greatly appreciated as I have been stuck with this loop for a week now!

Many thanks, Tamara

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```