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