Add column to dataframe based on value of other column [duplicate]-CodePudding

I have two dataframes:

    DF1 <- data.frame (col1  = c("a", "b", "c"),
                      col2 = c("4", "3", "6")
    )
    
    DF2 <- data.frame (col3  = c("x", "y", "z"),
                       col4 = c("18", "3", "5")
    )

    


 DF1
     col2   col2
    1    a      4
    2    b      3
    3    c      6

     
    DF2
    col3 col4
    1    x   18
    2    y    3
    3    z    5

For each row I want to add DF2$col3 to DF1, if DF2$col4 has the same value as DF1$col2.

Same value <- copy x/y/z to new column in DF1

Different value <- write NA to new column in DF1

How can I do this?

CodePudding user response：

Is this what you need?

DF1$new <- ifelse(as.numeric(DF1$col2) == as.numeric(DF2$col4),
                  DF2$col3,
                  NA)

Result:

DF1
  col1 col2  new
1    a    4 <NA>
2    b    3    y
3    c    6 <NA>

CodePudding user response：

This is a merge operation.

merge(DF1, DF2, by.x="col2", by.y="col4", all.x = TRUE)
#   col2 col1 col3
# 1    3    b    y
# 2    4    a <NA>
# 3    6    c <NA>

Or a match operation:

DF1$col3 <- DF2$col3[match(DF2$col4, DF1$col2)]
DF1
#   col1 col2 col3
# 1    a    4 <NA>
# 2    b    3    y
# 3    c    6 <NA>

CodePudding user response：

library(tidyverse)
DF1 %>%
  left_join(., DF2, by = c('col2' = 'col4'))

which gives

#   col1 col2 col3
# 1    a    4 <NA>
# 2    b    3    y
# 3    c    6 <NA>