Programming

Hi,

I have two files formatted as following:

File 1: (user_num_ID , realID) (the NR here is 41671)

Code:

1  cust_034_60
2  cust_80_91
3  cust_406_4

..
..

File 2: (realID , clusterNumber) (total NR here is 1000)

Code:

cust_034_60  2
cust_406_4   3
..
..

and i want to compare these two files based on File 1 $2 field and File 2 $1 field and get a resulting file like

File 3: (user_num_ID, realID, clusterNumber)

Code:

1 cust_034_60 2
3 cust_406_4 3
..
..
..

just to summarize:
Create a new file3
Find where file2 ($1) is equal to file1($2)
and print to file3 file1($1) and file2($1,$2) (as a single record)


since im new in awk, i've tried several suggestions from previous threads but it seems that im doing something wrong...

the latest one I've tried:

Code:

awk > file3 'NR==FNR{ _[$2]=$1 next}{print $0, _[$1,$2] }' file1 file2

surely im doing something wrong

Thanks in advance

Moderator's Comments:

Video tutorial on how to use code tags in The UNIX and Linux Forums.

Code:

awk > file3 'NR == FNR {
  f2[$1] = $2; next 
  }
$2 in f2 {
  print $0, f2[$2]
  }' file2 file1

Hi radoulov,

Thank you for your quick response. I've tried the script you suggested and it seems that i get an empty file3...is there an issue on whether i'm using awk under cygwin? I'm sure that i have types exactly what you suggested.

Thanks again

ps: i've tried using grep -f by just comparing the real_custID of file2 with file1 and it worked fine..but i'm curious on how this can be done using awk.

No, this is not a Cygwin issue.

Consider the following (rigth now, I'm on Cygwin too):

This is the content of the two input files: file1 and file2:

Code:

% head file[12]
==> file1 <==
1  cust_034_60
2  cust_80_91
3  cust_406_4

==> file2 <==
cust_034_60  2
cust_406_4   3

This is what I get when I run the awk command:

Code:

% awk 'NR == FNR {
  f2[$1] = $2; next
  }
$2 in f2 {
  print $0, f2[$2]
  }' file2 file1
1  cust_034_60 2
3  cust_406_4 3

To debug further, try dumping the content of the array f2 and the content of file1:

Code:

% awk 'NR == FNR {
  f2[$1] = $2; next
  }
FNR == 1 {
  for (F in f2)
    printf "|%s| --> |%s|\n", f2[F], F
  }
{
  printf "|%s|\n", $2
  }' file2 file1
|2| --> |cust_034_60|
|3| --> |cust_406_4|
|cust_034_60|
|cust_80_91|
|cust_406_4|

Your output should be different than mine.

It worked perfectly well now

Thank you again radoulov, all the best!

Hi, all:

I roughly understand that this code first reads in a smaller file(file_2) and stores every line into an array f2.

Next, when it reads in the other bigger one, file_1, line by line, it checks each line's 2nd field against the array f2. If there is a match, it prints out the current line in process and an element from the array f2.

Code:

awk > file3 'NR == FNR {
  f2[$1] = $2; next 
  }
$2 in f2 {
  print $0, f2[$2]
  }' file_2 file_1

#==> file_2 <==
#cust_034_60 2
#cust_406_4 3
#
#==> file_1 <==
#1 cust_034_60
#2 cust_80_91
#3 cust_406_4
#
#==> OUTPUT:
#1 cust_034_60 2
#3 cust_406_4 3


But I have some difficulty to figure out:

1. how file_2's lines being stored into f2?

Use the 1st line of file_2 as an example, "fcust_034_60 2"
==> f2[$1]=$2

It looks to me, the code only put the 2nd field, which is the number 2, into the array's position $1, not the entire current line goes in there.

2. how f2's element being retrieved by the code
==> f2[$2]?

If it had just put a field in the 1st step,
how could the code use "fcust_034_60" now read in from file_1 to search against the array f2?

To me, "fcust_034_60" is even not in f2.
And in the previous step, seems to me, the code "f2[$1]=$2", just put $2 from the line in the $1 position of f2. How come when retrieved, it is from the position $2 of f2?

I am new here and awk is new to me too.
The book I have at hand is talking about using awk to process one single file only.

Using awk to process 2 or more files at a time seems will take me some get used to it.

Thanks to the other person here on the other page clarified the NR/FNR issue very well,
Now I have a vague impression about how awk uses NR/FNR to handle 2 files's comparison at a time.

Hopefully someone here will give me some hints to my questions above too. Thank you in advance.

Regards,

In this example:f2['cust_034_60']=2
f2 is the array, and yes, 'cust_034_60' is an array index
(not sure where you got fcust_034_60 however...)

See my previous statement