Use variable names in functions of dplyr

Question

I want to use variable names as strings in functions of dplyr. See the example below:

df <- data.frame(        color = c("blue", "black", "blue", "blue", "black"),        value = 1:5) filter(df, color == "blue") 

It works perfectly, but I would like to refer to color by string, something like this:

var <- "color" filter(df, this_probably_should_be_a_function(var) == "blue"). 

I would be happy, to do this by any means and super-happy to make use of easy-to-read dplyr syntax.

Answer 1

In the newer versions, we can use we can create the variables as quoted and then unquote (UQ or !!) for evaluation

var <- quo(color) filter(df, UQ(var) == "blue") #   color value #1  blue     1 #2  blue     3 #3  blue     4 

Due to operator precedence, we may require () to wrap around !!

filter(df, (!!var) == "blue") #   color value #1  blue     1 #2  blue     3 #3  blue     4 

With new version, || have higher precedence, so

filter(df, !! var == "blue") 

should work (as @Moody_Mudskipper commented)

Older option

We may also use:

 filter(df, get(var, envir=as.environment(df))=="blue")  #color value  #1  blue     1  #2  blue     3  #3  blue     4 

EDIT: Rearranged the order of solutions