Concatenate columns and add them to beginning of Data Frame

Question

Noob here to R. Trying to figure something out. I need to build a function that adds a new column to the beginning of a dataset. This new column is a concatenation of the va

Answer 1

paste0 works fine, with some help from do.call:

do.call(paste0, mydf[c(1, 3, 4)])
# [1] "bat1a" "cow2b" "dog3c"

Your function, thus, can be something like:

addPrimaryKey <- function(inDF, cols) {
  cbind(ID = do.call(paste0, inDF[cols]),
        inDF)
}

You may also want to look at interaction:

interaction(mydf[c(1, 3, 4)], drop=TRUE)
# [1] bat.1.a cow.2.b dog.3.c
# Levels: bat.1.a cow.2.b dog.3.c

Answer 2

This should do the trick

addPrimaryKey <-function(df, cols){

   q<-apply(df[,cols], 1, function(x) paste(x, collapse=""))

   df<-cbind(q, df)

   return(df)

}

Just add in some conditional logic for your nulls

Answer 3

Two other options for combining columns are dplyr::mutate() and tidyr::unite():

library(dplyr)

df %>%
  mutate(new_col = paste0(col1, col3, col4)) %>% 
  select(new_col, everything()) # to order the column names with the new column first


library(tidyr)

df %>% 
  unite(new_col, c(col1, col3, col4), sep = '', remove = FALSE)

The default argument in tidy::unite() is remove = TRUE, which drops the original columns from the data frame leaving only the new column.