Shell Programming and Scripting

Dear all,

I find a shell script about awk command in the forum regarding
"Find and replace duplicate column values in a row"

In this thread, there is a command line as shown below to replace duplicate

Code:

awk -F, '{for (i=1;i<=NF;i++){if (v[i,$i]++){b[$i]=$i;$i=""}};print $0}  END { print "dups are" ;for ( i in b) print i}' OFS=","  input_file

from input

Code:

1,2,3,4,5 a,b,c,d,e b,c,a,e,f a,b,e,a,h

to output

Code:

1,2,3,4,5
a,b,c,d,e
b,c,a,e,f
,,e,a,h
dups are
a
b

My question is that
1) Can any people explain this part shown above about the awk array? what does v[i,$i]++ mean?

==> if (v[i,$i]++){b[$i]=$i;$i=""}

Thank you so much

Regards,
Eldon

Moderator's Comments:

How to use code tags when posting data and code samples.

So v[i,$i] is a 2d array

so looking at a b c d e, v[i,$i] for the first field is v[1,a], v[1,a]++ would be 0 the first time. Later down with a b e a h,

v[i,$i] for first element becomes, v[1,a], v[1,a] gets incremented to 1, since this is the second time it has seen a in column 1.

if(v[1,a]++) gets evaluated to if(1), since v[1,a] is now 1 due to increment above.

Since '1' equates to true, the following gets evaluated :

b[$i]=$i;$i="", which makes b[a] = a and $1 field is set to " ". So in summary, it stores the duplicate values it finds in array b


This is the best I could do with the explanation. Hopefully it all makes sense . Maybe someone else can attempt and write a simpler explanation and correct anything I may have misstated.