How can I merge two files while printing a given value on resulting empty fields using AWK? - awk

Question

I have two files:
01File:
1 2051
2 1244
7 917
X 850
22 444
21 233
Y 47
KI270728_1 6
KI270727_1 4
KI270734_1 3
KI270726_1 2
KI270713_1 2
GL000195_1 2
GL000194_1 2
KI270731_1 1
KI270721_1 1
KI270711_1 1
GL000219_1 1
GL000218_1 1
GL000213_1 1
GL000205_2 1
GL000009_2 1
and 02File:
1 248956422
2 242193529
7 159345973
X 156040895
Y 56887902
22 50818468
21 46709983
KI270728_1 1872759
KI270727_1 448248
KI270726_1 43739
GL000009_2 201709
KI270322_1 21476
GL000226_1 15008
KI270311_1 12399
KI270366_1 8320
KI270511_1 8127
KI270448_1 7992
I need to merge these two files based on Field 01 and print "0"s on resulting empty fields.
I was trying to accomplish this using the following command:
awk 'FNR==NR{a[$1]=$2 FS $3;next}{ print $0 "\t" a[$1]}' 01File 02File
Which results in the following output:
1 248956422 2051
2 242193529 1244
7 159345973 917
X 156040895 850
Y 56887902 47
22 50818468 444
21 46709983 233
KI270728_1 1872759 6
KI270727_1 448248 4
KI270726_1 43739 2
GL000009_2 201709 1
KI270322_1 21476
GL000226_1 15008
KI270311_1 12399
KI270366_1 8320
KI270511_1 8127
KI270448_1 7992
However, I am having trouble adapting the command so as to be able to print, in this case a value of zero "0" on the resulting empty fields, so as to generate the following output:
1 248956422 2051
2 242193529 1244
7 159345973 917
X 156040895 850
Y 56887902 47
22 50818468 444
21 46709983 233
KI270728_1 1872759 6
KI270727_1 448248 4
KI270726_1 43739 2
GL000009_2 201709 1
KI270322_1 21476 0
GL000226_1 15008 0
KI270311_1 12399 0
KI270366_1 8320 0
KI270511_1 8127 0
KI270448_1 7992 0
I would be grateful if you can get me going in the right direction

Answer 1

Use a conditional expression in place of a[1]. Instead of the empty string, "0" will be printed if no line matched.
awk 'FNR==NR{a[$1]=$2;next} {print $0 "\t" ($1 in a? a[$1]: "0")}' 01File 02File
Also I simplified the first action, as there are only 2 fields.
Output:
1 248956422 2051
2 242193529 1244
7 159345973 917
X 156040895 850
Y 56887902 47
22 50818468 444
21 46709983 233
KI270728_1 1872759 6
KI270727_1 448248 4
KI270726_1 43739 2
GL000009_2 201709 1
KI270322_1 21476 0
GL000226_1 15008 0
KI270311_1 12399 0
KI270366_1 8320 0
KI270511_1 8127 0
KI270448_1 7992 0