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rdplyrrlangquosure

What's the difference between `as.name` and `sym`?

I'm trying to wrap my head around standard, non-standard evaluation, quosures, etc. In many examples, I see passed string variable being transformed into dplyr-usable form either with as.name or with sym of rlang package.

Are they interchangeable in pipes? What are the cases that will fail for one or the other?

Solution

  • EDIT: I could not readily create a scenario where as.name fails to work. Hadley seems to agree that as.name might work. Although this is using select which really is robust, trying with group_by and summarise appears to have no difference.

    Robust select:

     varName <- "Sepal.Length"
 select(iris, varName) #This works

    No difference between as.name and sym for several examples I run.

    iris %>%
    group_by(!!as.name(varName))
iris %>% 
    group_by(!!sym(varName))

    Attempts to change encoding:

    var1 <- `Encoding<-`(varName, "unknown")

    Both as.name and sym still worked.

    Original answer:

    From the docs?sym:

    These functions take strings as input and turn them into symbols.

    Contrarily to as.name(), they convert the strings to the native encoding beforehand.This is necessary because symbols remove silently the encoding mark of strings (see set_str_encoding()).

    It therefore seems that using sym and related functions eliminates the trouble to do with encoding.