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I am a recent convert to R and am struggling to find the R equivalent of the following: looping over variables named with a common prefix plus a number (var1, var2, ..., varn).

Say I have a dataset where each row is a store and each column is the value of that store's revenue in month 1, month 2...month 6. Some made-up data for example:

store = c("a", "b", "c", "d", "c") rev1 = c(500, 200, 600, 400, 1200) rev2 = c(260, 100, 450, 45, 1300) rev3 = c(500, 150, 610, 350, 900) rev4 = c(480, 200, 600, 750, 1000) rev5 = c(500, 68, 750, 350, 1200) rev6 = c(510, 80, 1000, 400, 1450) df = data.frame(store, rev1, rev2, rev3, rev4, rev5, rev6)

I am trying to do something like the following:

varlist <- paste("rev", 1:6) #create list of variables rev1-rev6 # for i in varlist { highrev[i] <- ifelse(rev[i] > 500, 1, 0) }

So for each existing variable rev1:rev6, create a variable highrev1:highrev6 which equals 1 if rev1:rev6 > 500 and 0 otherwise.

Can you suggest an appropriate means of doing this?

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3 Answers 3

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In R, we usually don't use loops for such operations. You could simply do:

df[paste0("highrev", 1:6)] <- (df[paste0("rev", 1:6)] > 500) + 0 df # store rev1 rev2 rev3 rev4 rev5 rev6 highrev1 highrev2 highrev3 highrev4 highrev5 highrev6 # 1 a 500 260 500 480 500 510 0 0 0 0 0 1 # 2 b 200 100 150 200 68 80 0 0 0 0 0 0 # 3 c 600 450 610 600 750 1000 1 0 1 1 1 1 # 4 d 400 45 350 750 350 400 0 0 0 1 0 0 # 5 c 1200 1300 900 1000 1200 1450 1 1 1 1 1 1
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4

setup

varlist <- paste0("rev",1:6) # note that this is paste0, not paste hvarlist <- paste0("hi",varlist)

data.table solution. There is a nice way to do this in data.table:

require(data.table) setDT(df)[,(hvarlist):=lapply(.SD,function(x)1L*(x>500)),.SDcols=varlist] # store rev1 rev2 rev3 rev4 rev5 rev6 hirev1 hirev2 hirev3 hirev4 hirev5 hirev6 # 1: a 500 260 500 480 500 510 0 0 0 0 0 1 # 2: b 200 100 150 200 68 80 0 0 0 0 0 0 # 3: c 600 450 610 600 750 1000 1 0 1 1 1 1 # 4: d 400 45 350 750 350 400 0 0 0 1 0 0 # 5: c 1200 1300 900 1000 1200 1450 1 1 1 1 1 1

The dplyr package is also designed with this sort of operation in mind...but simply cannot do it.

A bad alternative. Here's another way, hewing closely to the OP's loop:

within(df,{for(i in 1:6) assign(hvarlist[i],1L*(get(varlist[i]) > 500));rm(i)}) # store rev1 rev2 rev3 rev4 rev5 rev6 hirev6 hirev5 hirev4 hirev3 hirev2 hirev1 # 1 a 500 260 500 480 500 510 1 0 0 0 0 0 # 2 b 200 100 150 200 68 80 0 0 0 0 0 0 # 3 c 600 450 610 600 750 1000 1 1 1 1 0 1 # 4 d 400 45 350 750 350 400 0 0 1 0 0 0 # 5 c 1200 1300 900 1000 1200 1450 1 1 1 1 1 1

You can't assign to dynamic variable names with hvarlist[i] <- ...; this is done instead with assign(hvarlist[i],...), but using the latter is not a good habit. Similarly, get must be used to grab a variable on the basis of a string containing its name.

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1

If you want to keep the loop, you could try this

store = c("a", "b", "c", "d", "c") rev1 = c(500, 200, 600, 400, 1200) rev2 = c(260, 100, 450, 45, 1300) rev3 = c(500, 150, 610, 350, 900) rev4 = c(480, 200, 600, 750, 1000) rev5 = c(500, 68, 750, 350, 1200) rev6 = c(510, 80, 1000, 400, 1450) df = data.frame(store, rev1, rev2, rev3, rev4, rev5, rev6)

You don't need the ifelse like David points out since > is vectorized and will work on the entire data frame

df[, -1] > 500 # rev1 rev2 rev3 rev4 rev5 rev6 # [1,] FALSE FALSE FALSE FALSE FALSE TRUE # [2,] FALSE FALSE FALSE FALSE FALSE FALSE # [3,] TRUE FALSE TRUE TRUE TRUE TRUE # [4,] FALSE FALSE FALSE TRUE FALSE FALSE # [5,] TRUE TRUE TRUE TRUE TRUE TRUE

Here is your loop slightly amended

for (i in 1:6) { x <- paste0('rev', i) y <- paste0('highrev', i) df[, y] <- (df[, x] > 500) + 0L } # store rev1 rev2 rev3 rev4 rev5 rev6 highrev1 highrev2 highrev3 highrev4 highrev5 highrev6 # 1 a 500 260 500 480 500 510 0 0 0 0 0 1 # 2 b 200 100 150 200 68 80 0 0 0 0 0 0 # 3 c 600 450 610 600 750 1000 1 0 1 1 1 1 # 4 d 400 45 350 750 350 400 0 0 0 1 0 0 # 5 c 1200 1300 900 1000 1200 1450 1 1 1 1 1 1
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2 Comments

@Frank but without it, my answer is not reproducible. I hate it when someone answers a question and I cannot copy/paste to get their result.
Okay, I guess it's a matter of taste; I always run the OP's example before trying questions.

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