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

I just love R, here is yet another Base R solution but with mapply:

data.frame(mapply(c, df1, df2))

Result:

  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

Note:

No need to deal with colnames like almost all the other solutions... The key to why this works is that "mapply calls FUN for the values of ... [each element] (re-cycled to the length of the longest...[element]" (See ?mapply). In other words, df2$A is recycled to however many columns df1 has.

Data:

df1 = structure(list(A = c(1L, 5L), B = c(2L, 7L), C = c(3L, 9L)), .Names = c("A", 
                                                                               "B", "C"), class = "data.frame", row.names = c(NA, -2L))
df2 = structure(list(A = 1:4), .Names = "A", row.names = c(NA, -4L), class = "data.frame")