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I am trying to assign different window sizes to my SNPs dataset to identify regions under selection.

this is the head of my data

head(snp_ids)
   snp_id   chr  pos
Chr01__912    1  912
Chr01__944    1  944
Chr01__1107   1 1107
Chr01__1118   1 1118
Chr01__1146   1 1146
Chr01__1160   1 1160

class(snp_ids)
data.frame

I have chosen 4 different window sizes, win_size <- c(15000, 30000, 50000, 100000). I have assigned each of these different window sizes to my snp_ids dataset to identify how many SNPs are distributed within each window by looping through each window size 

for (i in 1:length(win_size)){
  windows <- sapply(snp_ids$pos, function(x) (ceiling(x/win_size[i])))
}
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    $\begingroup$ I would like to help, but do not completely follow. I am not sure what you're trying to do. Furthermore, if you want help with code, you should provide a minimal data set to work with (for us to test it). $\endgroup$
    – benn
    Nov 20, 2017 at 20:07
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    $\begingroup$ How are you getting 1.2 for window_30000? $\endgroup$
    – zx8754
    Nov 21, 2017 at 8:27
  • $\begingroup$ @Anna To help others you can post your own answer to the question. But please do not include it in the question body (unless they are unsuccessful attempts) $\endgroup$
    – llrs
    Nov 30, 2017 at 8:49

2 Answers 2

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Not clear what we are trying to do, but here is the solution using lapply that should replicate your existing forloop.

# example input data
snp_ids <- read.table(text = "
snp_id  chr  pos
Chr01__912   1  912
Chr01__944   1  944
Chr01__1107  1 1107
Chr01__1118  1 1118
Chr01__1146  1 1146
Chr01__1160  1 1160", header = TRUE)

# window sizes to loop through
win_size <- c(15000, 30000, 50000, 100000)

res <- cbind(snp_ids,
             data.frame(
               lapply(setNames(win_size, paste("window", win_size, sep = "_")), function(w)
                 as.numeric(paste(snp_ids$chr, ceiling(snp_ids$pos/w), sep = "."))
               )))

# result
res
#        snp_id chr  pos window_15000 window_30000 window_50000 window_1e.05
# 1  Chr01__912   1  912          1.1          1.1          1.1          1.1
# 2  Chr01__944   1  944          1.1          1.1          1.1          1.1
# 3 Chr01__1107   1 1107          1.1          1.1          1.1          1.1
# 4 Chr01__1118   1 1118          1.1          1.1          1.1          1.1
# 5 Chr01__1146   1 1146          1.1          1.1          1.1          1.1
# 6 Chr01__1160   1 1160          1.1          1.1          1.1          1.1

Edit: If we really want to use forloop, then try below:

for (i in win_size){
  windows <- ceiling(snp_ids$pos/i)
  snp_ids[, paste0("window_", i)] <- as.numeric(paste(snp_ids$chr, windows, sep = "."))
}
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2
  • $\begingroup$ thanks so much @zx8754. I have edited my post a bit and hope it is more understandable. Your code worked for me. But, as I am learning R programming I wanted to know is there any other way that I could fix my own code above? Thanks so much for your help. $\endgroup$
    – Anna1364
    Nov 21, 2017 at 20:12
  • $\begingroup$ @Anna1364 See edit, yes we could use forloop but I prefer apply family. $\endgroup$
    – zx8754
    Nov 21, 2017 at 21:43
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This explicitly doesn't use apply() or lapply(), but rather the dplyr package. This is probably easier to read and debug:

library("dplyr")
snp_ids %>% mutate(window_15000=as.numeric(paste(chr, ceiling(pos/15000), sep=".")),
                   window_30000=as.numeric(paste(chr, ceiling(pos/30000), sep=".")),
                   window_50000=as.numeric(paste(chr, ceiling(pos/50000), sep=".")),
                   window_100000=as.numeric(paste(chr, ceiling(pos/100000), sep=".")))
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    $\begingroup$ This is a bit manual, don't you think? $\endgroup$
    – zx8754
    Nov 21, 2017 at 11:24
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    $\begingroup$ Manual and clear is easier to debug and understand 6 months later (one could also put most of that in a function to make it shorter). $\endgroup$
    – Devon Ryan
    Nov 21, 2017 at 11:26
  • $\begingroup$ Of course, personal preferences. But if there were 100 windows, that change by 500 bases for each window in 6 month time. $\endgroup$
    – zx8754
    Nov 21, 2017 at 11:45
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    $\begingroup$ Manual isn’t the problem — having duplication is. If I had to write this code, five times out of ten (at least!) I’d make a typo in at least one of the numbers, leading to mismatches between the column names and their actual values. That’s why we automate. (I’m saying “I” but what I really mean is “the average, competent programmer”; this class of mistakes is incredibly common). $\endgroup$
    – Konrad Rudolph
    Nov 22, 2017 at 16:24
  • $\begingroup$ A couple lines of code duplication is a nonissue. If someone neede to add a hundred columns then sure, but for three then trivial intelligibility is more useful. $\endgroup$
    – Devon Ryan
    Nov 22, 2017 at 16:45

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