How to pass a column name into a custom function, which uses dplyr?

Question

I've written this function which just replaced each value in a data table's column with its substring:

substrColName <- function(df, colName, start) { df %>% mutate(colName = substr(colName, start=start, stop=nchar(colName))) }

But every time I try running it I get the error:

Error in as.character(x) : cannot coerce type 'closure' to vector of type 'character'

Now I've done a lot of research on why it won't work but I can't figure it out. I've read on some stuff with standard evaluations and lazyeval but nothing I try seems to work. Any help?

Thanks

Can you provide the data with which you ran the function on? — acylam
– acylam, Commented Oct 7, 2017 at 2:57
See this cran.r-project.org/web/packages/dplyr/vignettes/… to learn programming with dplyr. — www
– www, Commented Oct 7, 2017 at 3:02

gupta · Accepted Answer · 2017-10-07 04:28:25Z

Thanks, @ycw, that was a nice read. Got it working now after working through the article. This was the solution at the end of the day:

substrColName <- function(df, colName, start) { colNameQuo <- enquo(colName) df %>% mutate(!!quo_name(colNameQuo) := substr(!!colNameQuo, start=start,stop=nchar(!!colNameQuo))) }

And this is ycw's comment.

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