JerryN JerryN - 10 days ago 5
R Question

r data table Map warning 'longer argument not a multiple of length of shorter'

My question is about the warning I sometimes get with the code. The warning is

Warning message:
In mapply(FUN = f, ..., SIMPLIFY = FALSE) :
longer argument not a multiple of length of shorter


The idea seems simple. I want to multiple the values in each row of a vector of column names (cn) by those in the same row of another column and replace the cn columns with the new values. I'm constructing weighted sums. The weights are foodAvailRatio.

dt.temp <- readRDS("xxx")
cn <- c("usda_code", "item", "foodAvailRatio","item_name", "usda_desc", "IMPACT_code", "Ref_Desc", "RetnDesc", "retentioncode_aus")
cm <- names(dt.temp)[!names(dt.temp) %in% cn]
# multiply all the columns in cm by foodAvailRatio and assign to the cm columns
dt.temp[, (cm) := Map(`*`, mget(cm), foodAvailRatio)]


With this replacement (dt.cocer.rds) for xxx, don't get the error. With a different one (dt.vege.rds) I get the error. Both have length 52. For both sum(foodAvailRatio) = 1.

I'm doing this in RStudio with Microsoft Open R v 3.3.1 on a mac.

Answer

I believe you're trying to multiply all the cm columns by foodAvailRatio?

Try this:

dt.temp[ , (cm) := lapply(.SD, `*`, foodAvailRatio), .SDcols = cm]

Note that using foodAvailRatio like this will require the development version (installation instructions here) since it's not in .SDcols.

In 1.9.6 (currently on CRAN), you can replace foodAvailRatio with dt.temp$foodAvailRatio.

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