converting FOR loop to apply in R

Question

I'm trying to learn how to use apply, but am getting a bit stuck. This loop is converting all of the columns (except the first four) to their accumulated sums.

Can anyone help me? Thanks!

for (i in seq_along(newbuilds.byfuel.bydate)) {
  if (i >= 5) {
    newbuilds.byfuel.bydate[i] <- cumsum(newbuilds.byfuel.bydate[i])

  }
}

Is `newbuilds.byfuel.bydate` a data.frame? Make sure to provide a [reproducible example](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) when asking for help. That will make it easier to help you. — MrFlick, Apr 03 '17 at 15:24

Zelazny7 · Answer 1 · 2017-04-03T16:14:01.523

2

This is how I would do this if your object is a data.frame:

## dummy dataset
x <- mtcars

Use lapply to loop over the desired columns, calculate the cumsum, and then overwrite the original columns:

x[5:ncol(x)] <- lapply(x[5:ncol(x)], cumsum)

Alternatively, loop over the un-dropped columns:

x[-(1:4)] <- lapply(x[-(1:4)], cumsum)

edited Apr 03 '17 at 16:14

answered Apr 03 '17 at 15:38

Zelazny7

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To avoid typing the col indices twice, I'd either define it as a separate variable or do something weird like `do.call(transform, c(list(x), lapply(x[-(1:4)], cumsum)))` – Frank Apr 03 '17 at 16:09
Looks like this works as well: `transform(x, lapply(x[-(1:4)], cumsum))` – Zelazny7 Apr 03 '17 at 16:11
That seems to have no effect on the cols..? – Frank Apr 03 '17 at 16:13
1

You're right. I made a rookie mistake by not rerunning my entire script. – Zelazny7 Apr 03 '17 at 16:15

converting FOR loop to apply in R

1 Answers1