Find variable name and use it to create a new variable name-CodePudding

I need to find the column called "L1_Class" but only using the 'node' object defined first. Then, I'd like to add a column called "L1" that contains the same vector as "L1_Class". All in one short line if possible.

library(dplyr)

node <- "L1" # (in real life this is a folder name in a working directory) "../Mapping/VegType/L1" 

# test dataframe
dat <- data.frame(L1_Class = c(rep("veg", 3), 
                               rep("rock", 4), 
                               rep("snow", 2)),
                  L2_tree = c(rep("conifer", 3), 
                               rep("cottonwood", 4), 
                               rep("snow", 2)),
                  L2_shrub = c(rep("alder", 3), 
                              rep("willow", 4), 
                              rep("snow", 2)),
                  L3_tree = c(rep("alder", 3), 
                               rep("willow", 4), 
                               rep("snow", 2)))

# this is what I need to add only using a function.
dat$L1 <- dat$L1_Class

# end dataframe (i hope).
head(dat)

# I need to find the column called "L1_Class" but only using the 'node' object. 
# Then, I'd like to add a column called "L1" that contains the same vector as "L1_Class"
# All in one short line if possible.

dat_extra_col <- dat %>%
         mutate( across(starts_with(gsub('_[^_]*$', "", node, fixed = TRUE))), .fns = list(node = ~gsub('_[^_]*$', "", ., fixed = TRUE)))

# or worse

dat_extra_col 
dat %>% mutate(!!node := across(starts_with(gsub('_[^_]*$', "", node, fixed = TRUE))))

Thanks for any help!

CodePudding user response：

If it is always the first part of the column name and does not need to handle duplicates then you can use substr() to select the first n characters and match() to find the column of interest.

dat[[node]] <- dat[,!is.na(match(substr(colnames(dat), 1, nchar(node)), node))]

CodePudding user response：

You can use -

dat[[node]] <- dat[[paste0(node, '_Class')]]

dat

#  L1_Class    L2_tree L2_shrub L3_tree   L1
#1      veg    conifer    alder   alder  veg
#2      veg    conifer    alder   alder  veg
#3      veg    conifer    alder   alder  veg
#4     rock cottonwood   willow  willow rock
#5     rock cottonwood   willow  willow rock
#6     rock cottonwood   willow  willow rock
#7     rock cottonwood   willow  willow rock
#8     snow       snow     snow    snow snow
#9     snow       snow     snow    snow snow

This creates a new column named node copying the data from node _Class.

Or using grep if not all variables have _Class as suffix.

dat[[node]] <- dat[[grep(node, names(dat))]]