Split R vector into even size chunks

Question

This seems like it should be trivial, but the results are unexpected

# create empty list
list=c()
# create vector of one hundred 4s
fours=rep(4,100)
# for loop. Try to split into 10
for(i in seq(10)){
  # split into chunks: i=1, take fours[1:10]; i=2, fours[11:20]...
  # when i=10, should return fours[91:100]
  chunks=fours[1+10*(i-1):10*i]
  # add smaller lists of four back into bigger list
  list=c(list,chunks)
}
list
# returns  [1]  4  4  4  4  4  4  4  4  4  4 NA  4  4  4  4 NA NA NA NA NA NA  4  4 NA NA
[26] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA

I would expect to just get back one hundred 4 values.

from my first look, one dark mistake we all do is misisng out those `()` when having arithmetic operators aroung `:` while subsetting. — joel.wilson, Jan 22 '17 at 17:40

rnso · Answer 1 · 2017-01-23T01:35:56.640

0

Following line needs to be corrected (parentheses to be added for proper arithmatic operation):

chunks=fours[1+10*(i-1):10*i]

Corrected code:

fours=rep(4,100)
chunks = list()
for(i in 1:10){
    chunks[[i]] = fours[(1+((i-1)*10)) : (10+((i-1)*10))]
}
chunks

Or:

fours=rep(4,100)
chunks = list()
for(i in 1:10){
    start = 1+((i-1)*10)
    chunks[[i]] = fours[ start : (9+start)]
}
chunks

Ouput:

[[1]]
 [1] 4 4 4 4 4 4 4 4 4 4

[[2]]
 [1] 4 4 4 4 4 4 4 4 4 4

[[3]]
 [1] 4 4 4 4 4 4 4 4 4 4

[[4]]
 [1] 4 4 4 4 4 4 4 4 4 4

[[5]]
 [1] 4 4 4 4 4 4 4 4 4 4

[[6]]
 [1] 4 4 4 4 4 4 4 4 4 4

[[7]]
 [1] 4 4 4 4 4 4 4 4 4 4

[[8]]
 [1] 4 4 4 4 4 4 4 4 4 4

[[9]]
 [1] 4 4 4 4 4 4 4 4 4 4

[[10]]
 [1] 4 4 4 4 4 4 4 4 4 4

edited Jan 23 '17 at 01:35

answered Jan 22 '17 at 17:37

rnso

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Thanks...but two more questions: 1) length(list)=110. We want 100. Why the difference? 2) Why that last NA value? – William Nowak Jan 22 '17 at 17:42
check your output, it's not giving the expected output: `list` is 110 values long and ending with an `NA` – Jaap Jan 22 '17 at 17:42
Adding parentheses is the basic problem here. The values can be corrected taking into account the parentheses. – rnso Jan 22 '17 at 17:53
I have added corrected code above. – rnso Jan 22 '17 at 18:06

Split R vector into even size chunks

1 Answers1