rdynamictidyversemutate

Count number of characters with column name in dynamic variable

Provided that here there is written that I can pass {{colname}} to mutate, where colname is a variable that contains a column name, I cannot figure out why this code doesn't work:

testdf <- data.frame(a=c("Hello", "Hi", "Howy"))
varname <- "a"
testdf %>% mutate(b=nchar({{varname}}))

It returns the number of characters in the letter a:

      a b
1 Hello 1
2    Hi 1
3  Howy 1

How can I count the number of characters in a column and assign the value to another column, when the name of the first column is saved into a variable?

Solution

  • The issue arises because {{varname}} doesn't evaluate to the content of the variable varname when you use it inside mutate().

    In this case, {{varname}} is treated literally, which is why you're only seeing 1 for each row.

    To solve this, you can simply use base R for a straightforward solution. Here’s how you can do it:

    # Create a data frame
testdf <- data.frame(a = c("Hello", "Hi", "Howy"))

# Variable storing column name
varname <- "a"

# Use base R to add a column `b` with character counts
testdf$b <- nchar(testdf[[varname]])

    OUTPUT

          a  b
1 Hello  5
2    Hi  2
3  Howy  4