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R data.table applies a function to the sum of two columns

I have a data.table and I would like to apply a function on its columns. This is usually done as follows:

dt[, lapply(.SD, func), .SDcols = c("col1", "col2")]

And this will apply the function func

to those two columns. What if, however, I would like to apply it on the sum of these two columns? Something like

dt[, lapply(.SD, func), .SDcols = "col1 + col2"]

obviously doesn't work.

You can generalize this to apply func

another function (in this case, sum

) to the result that takes columns as arguments. I know I can create another column containing the results of the first function, but is there a way around this?

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1 answer


To add columns try

dt[, func(Reduce(`+`,.SD)), .SDcols = c("col1","col2")]


This works with more than two columns, adding them all together before applying func

.

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