Conditional replacement of string with another string

Question

I have the following structure of the data with all variables being in the string format:

    v1      v2      c1      c2           c1c2
00035A  943567  00088         


        

Answer 1

There is also an alternative approach using update in a self-join

library(data.table)
#coerce to data.table
setDT(df)[
  # 1st self join & update
  df, on = .(v1 = c1), v1 := c1c2][
    # 2nd slef join & update
    df, on = .(v2 = c2), v2 := c1c2][]

               v1            v2     c1     c2          c1c2
 1:        00035A        943567 00088E 63968E 00088E;63968E
 2: 00088E;63968E 00088E;63968E 00088E 63968E 00088E;63968E
 3: 00088E;63968E        925524 00088E 63968E 00088E;63968E
 4:        000361        237924 00088E 63968E 00088E;63968E
 5:        000361        83367A 00088E 63968E 00088E;63968E
 6:        00055X        49328R 00088E 63968E 00088E;63968E
 7:        00056N        87885Q 00088E 63968E 00088E;63968E
 8:        000794        69911G 00088E 63968E 00088E;63968E
 9:        23792A        001674 00088E 63968E 00088E;63968E
10:        63968E        17275R 00088E 63968E 00088E;63968E

Caveat