How to pass dynamic column names in dplyr into custom function?

by

Using the latest version of dplyr (>=0.7), you can use the rlang !! (bang-bang) operator.

library(tidyverse)
from <- "Stand1971"
to <- "Stand1987"

data %>%
  mutate(diff=(!!as.name(from))-(!!as.name(to)))

You just need to convert the strings to names with as.name and then insert them into the expression. Unfortunately I seem to have to use a few more parenthesis than I would like, but the !! operator seems to fall in a weird order-of-operations order.

Original answer, dplyr (0.3-<0.7):

From that vignette (vignette("nse","dplyr")), use lazyeval’s interp() function

library(lazyeval)

from <- "Stand1971"
to <- "Stand1987"

data %>%
  mutate_(diff=interp(~from - to, from=as.name(from), to=as.name(to)))

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