I have two tables with different numbers of columns and rows. I want to find rows using a common column (column B is in common). Here is an example. Could you please help?


A  B    C   D
a  b    c   d
i  ii  iii iV
*  **   #  ##


E  B  
f  ff 
h  b
g  gg
k  ii


A  B    C   D  E
a  b    c   d  h
i  ii  iii iV  k
  • 2
    Could you explain what you are doing in a bit more detail please? Why is the last line of file1 not in the output? And why is column B unchanged in the output while column E is added? – terdon Dec 17 '18 at 11:59
  • @terdon: I have two tables including some parameters of many galaxies. Assume table one include "mass" , "name","color" and "distance" of galaxies and table 2 include "velocity" and "name". . some galaxies are in common so have same name (column B). Now, I want to have all parameters for this galaxies in one table. – Negar Dec 17 '18 at 12:46

You can do this kind of thing by building a hash / associative array / lookup table e.g. using Awk:

$ awk 'NR==FNR{B[$2]=$1; next} $2 in B {print $0,B[$2]}' file2.txt file1.txt
A  B    C   D E
a  b    c   d h
i  ii  iii iV k

There's also the join command - but that requires inputs to be sorted on the common field.

  • It works. Thanks, but it doesn't print all columns of file1. could you please tell me how can I print all columns? – Negar Dec 17 '18 at 15:11
  • @Negar it should print all of the original columns from file1.txt (since $0 in Awk represents the whole record) - is there something additional about your actual files that you forgot to mention? – steeldriver Dec 17 '18 at 15:26
  • @ steeldriver It works right. I made a small mistake. Thanks – Negar Dec 18 '18 at 0:55

To add to the answer by @steeldriver, to do it with sort and join:

join -j 2 -o 1.1,0,1.3,1.4,2.1 <(sort -k 2 file1.txt)  <(sort -k 2 file2.txt)
  • -j 2 tells join which field is the key.
  • -o gives the order of the fields in the output, where 0 is the common key, and the others are FILENUM.FIELD. See man join for details.
  • -k 2 tells sort which field is the key.
  • <( ) is bash process substitution.

Output is:

a b c d h
i ii iii iV k
  • 1
    You may find that the column header position can be preserved by enforcing an appropriate locale e.g. LC_COLLATE=C sort ... – steeldriver Dec 17 '18 at 14:16
  • @Christoffer Hammarström: Thanks. could you please explain about 1.1, 0 ,1.3 ,... since my file1 has 13 columns and this command don't print all of them. – Negar Dec 17 '18 at 15:13
  • @Negar: Edited. See man join for further details. – Christoffer Hammarström Dec 17 '18 at 15:17

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