How assign the value

Maybe I'm misundertanding your issue but just to be sure, Do you mean that inside your colors variable you have text values like "c+1" and you want to convert them to 1?

If that is the case then you can do it like this


# Sample data on a copy/paste friendly format, replace whit your own data
addition_colors <- data.frame(
    stringsAsFactors = FALSE,
    colors = c("c+2", "c+4", "c+7")

addition_colors %>% 
    mutate(colors_calc = as.numeric(str_extract(colors, "\\d+$")))
#>   colors colors_calc
#> 1    c+2           2
#> 2    c+4           4
#> 3    c+7           7

Created on 2020-10-16 by the reprex package (v0.3.0)

If this doesn't solve your problem, please provide a proper REPRoducible EXample (reprex) illustrating your issue.