How to append group row into dataframe

Question

I have this df1:

A B C
1 2 3
5 7 9

where A B C are columns names.

I have another df2 with one column:

A
1
         


        

Answer 1

By analogy with @useR's excellent Base R answer, here's a tidyverse solution:

library(purrr)

map2_df(df1, df2, c)

  A B C
1 1 2 3
2 5 7 9
3 1 1 1
4 2 2 2
5 3 3 3
6 4 4 4

Here are a few other (less desirable) options from when I first answered this question.

library(dplyr)

bind_rows(df1, df2 %>% mutate(B=A, C=A))

Or, if we want to dynamically get the number of columns and their names from df1:

bind_rows(df1,
          df2[,rep(1,ncol(df1))] %>% setNames(names(df1)))

And one more Base R method:

rbind(df1, setNames(df2[,rep(1,ncol(df1))], names(df1)))