dplyr::group_by_ with character string input of several variable names

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No need for interp here, just use as.formula to convert the strings to formulas:

dots = sapply(y, . %>% {as.formula(paste0('~', .))})
mtcars %>% group_by_(.dots = dots)

The reason why your interp approach doesn’t work is that the expression gives you back the following:

~list(c("cyl", "gear"))

– not what you want. You could, of course, sapply interp over y, which would be similar to using as.formula above:

dots1 = sapply(y, . %>% {interp(~var, var = .)})

But, in fact, you can also directly pass y:

mtcars %>% group_by_(.dots = y)

The dplyr vignette on non-standard evaluation goes into more detail and explains the difference between these approaches.

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