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using join command for files

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Special Forums Hardware Filesystems, Disks and Memory using join command for files
# 8  
Old 08-13-2002
Hi Subra,

could you post back the content of the files you like to join.


# 9  
Old 08-13-2002
You can acheive this with a combination of awk and join.

File_one has 4 columns "first name, lastname, age, height"
File_two has 3 columns "first name, lastname, weight"

You want the output to have "first name, lastname, age, height, weight" - for only those records with a weight present - and your key is first and last name.

awk '
BEGIN { OFS = "," } { print $1 $2 , $1, $2, $3 ,$4 } 
' File_one > temp_File_one 
awk '
BEGIN { OFS = "," } { print $1 $2 , $1, $2, $3 } 
' File_two> temp_File_two
join -t ","  -j1 1 -j2 1 -o 1.2 1.3 1.4 1.5 2.4  temp_File_one temp_File_two > File_three

# 10  
Old 08-14-2002

The above code is working perfectly...

I have heard of IFS(Internal Field Seperator)... Could you please tell me what OFS is????

And also i am new to this join command....

can u explain this to me....

join -t "," -j1 1 -j2 1 -o 1.2 1.3 1.4 1.5 2.4 temp_File_one temp_File_two

The join command works even like this..

join -t "," -o 1.2 1.3 1.4 1.5 2.4 temp_File_one temp_File_two

A few other questions...

1. Why do i need two temp files at all??
2. Why can't I directly join the file_one and file_two?
3. Why should there be a statement like this ?
BEGIN { OFS = "," } { print $1 $2, $1, $2, $3 ,$4 }
instead of
BEGIN { OFS = "," } { print $1, $2, $3 ,$4 }


Last edited by Nisha; 08-14-2002 at 03:19 AM..
# 11  
Old 08-14-2002
Hi Nisha,

one of your other questions I think Im able to answer.

2. Why can't I directly join the file_one and file_two?

You can Join them directly but then you can only join them by one column.

So what Peter did was to concatenate the "firstname" & "lastname" column for both files

(And this explains the first of your other questions
1. Why do i need two temp files at all?? )

The third questionI ll try to answer as well
3. Why should there be a statement like this ?
BEGIN { OFS = "," } { print $1 $2, $1, $2, $3 ,$4 }

this lines output will be

BEGIN { OFS = "," } { print $1, $2, $3 ,$4 }


After that he was able to join those both files based on two columns, whats not exactly correct, cause he joined them based on one column in what the keycolumns has benn concatenated.

the Output of the second statement is

Did I get that right?
# 12  
Old 08-14-2002
Directly from the man page

OFS output field separator (default blank)

The reason for the { print $1 $2, $1,$2,$3,$4 } and the reason for having 2 temp files is the same. Join will only allow you to join on one field. In this instance we want to join on two fields.

So we make a composite key by concatenating the two fields into one string and apending that at the start of the each line - we do this for both files.

Then we can join using one field - being the composite key.

i.e. To join where column 1 and 5 are the same in both files

File1 before is

File2 before is "

The files with the {print $1 $5, $0} (you know what $0 is too...)

File1 before is

File2 before is "

So we have the composite key matching the aaa333 in both files - and we can join on this with and make sure in our output there's not 1.1 or 2.1 (which would be the first fields from each file - as they are the fields we created and don't want to see again)

Just seen your reply while entering mine isacs!
# 13  
Old 08-14-2002
Thanks Peter and Isacs for the replies...

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