Create a new categorical column merging two categorical columns-CodePudding

I have this df

df <- data.table(id=c(1,2,3,4,5,6,7,8,9,10),
                 var1=c(0,4,5,6,99,3,5,5,23,0),
                 var2=c(22,4,6,25,6,70,75,23,24,21))

I would like to create a third column being:

df <- data.table(id=c(1,2,3,4,5,6,7,8,9,10),
                 var1=c(0,4,5,6,99,3,5,5,23,0),
                 var2=c(22,4,6,25,6,70,75,23,24,21),
                 var3=c("0_22","4_4","5_6","6_25","99_6","3_70","5_75","5_23","23_24","0_21"))

where the value of each cell will be "var1 underscore var2". Var1 and Var2 are categorical variables as they represent medications. Var3 would be to represent a combination of medications.

how can I do this?

thanks!

CodePudding user response：

Load packages

library(data.table)
library(dplyr)

Create dataframe

df <- data.table(
  id = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10),
  var1 = c(0, 4, 5, 6, 99, 3, 5, 5, 23, 0),
  var2 = c(22, 4, 6, 25, 6, 70, 75, 23, 24, 21)
)

Add new variable

By means of dplyr package and sprintf

df <- df %>% 
  mutate(var3 = sprintf("%d_%d", var1, var2))

By means of dplyr package and paste0

df <- df %>% 
  mutate(var3 = paste0(var1, "_", var2))

By means of base package and sprintf

df$var3 <- sprintf("%d_%d", df$var1, df$var2)

By means of base package and paste0

df$var3 <- paste0(df$var1, "_", df$var2)

CodePudding user response：

as @Wimpel says, the solution is df$var3 <- paste(df$var1, df$var2, sep = "_") thanks!!

CodePudding user response：

You can do this efficiently using the tidyverse and the unite() function

library(tidyverse) 

df <- tibble(id=c(1,2,3,4,5,6,7,8,9,10),
                 var1=c(0,4,5,6,99,3,5,5,23,0),
                 var2=c(22,4,6,25,6,70,75,23,24,21)) %>%
  # create new variable
  unite(var3, c(var1, var2), sep = "_", remove = FALSE)