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Option to pick last 5 records from flat file

 
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hamsalakshmi

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Joined: 30 Aug 2010
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PostPosted: Mon Sep 20, 2010 1:48 pm    Post subject: Option to pick last 5 records from flat file
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Hi,

Ineed to get last 5 records from a flat file and the output file should have that 5 records.
For this scenario i need to code a COBOL program.

Do we have the option to get last 5 records from a flat file?
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enrico-sorichetti

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PostPosted: Mon Sep 20, 2010 2:48 pm    Post subject: Reply to: Option to pick last 5 records from falt file.
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do You have a doctor' s prescription to be forced to use COBOL ???

search the <sort> forums for samples on how to do it

anyway here is a snippet to be tested


Code:
//S1    EXEC  PGM=ICETOOL                           
//SYSOUT    DD  SYSOUT=*                           
//DFSMSG    DD  SYSOUT=*                           
//TOOLMSG    DD  SYSOUT=*                           
//IN DD  DSN=YOUR INPUT HERE                               
//OUT DD DSN=YOUR OUTPUT HERE
//TOOLIN DD *                                       
  SUBSET FROM(IN) TO(OUT) KEEP INPUT LAST(<number of records to be kept>)       
/*                                                 
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nareshkp

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Joined: 26 Sep 2007
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PostPosted: Mon Sep 20, 2010 3:12 pm    Post subject:
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If you are forced to use a COBOL program, you can consider the following approach:

1. Define a working storage table for 5 occurences with input record format.
2. Read the input file into the WS-table. Over-write from the first occurence when the WS-table is filled up.
3. At the end of the input file, you will have the last 5 records in WS-table. Write them into output file.

But remember, the 5 records in the output file may or may not be in the same order.
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Anuj Dhawan

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Joined: 22 Apr 2006
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PostPosted: Mon Sep 20, 2010 3:20 pm    Post subject:
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Well, the requirements!

Do you have file on Tape? If yes, look at REVERSE verb in COBOL Manual.

If tape-file is multi-volume - REVERSE might or might not work. But just for five records I'd, probably, ignore the fact of file being multi-volume. (It's a dangerous and not-so-technical assumption tough; but OP has not talked about the approx. records on file - so I'll take the benefit of doubt.)

It should be noted that manual says:
Quote:
REVERSED
Valid only for sequential single-reel files. REVERSED is not valid for VSAM files.

If the concept of reels has no meaning for the storage medium (for example, a direct access device), the REVERSED and NO REWIND phrases do not apply.

NO REWIND
Valid only for sequential single-reel files. It is not valid for VSAM files.
Though OPEN REVERSED is obsolete according to the COBOL standards committee. The option has not been made obsolete by IBM in its COBOL. so, possibly you stand a chance.
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Phrzby Phil

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PostPosted: Mon Sep 20, 2010 5:16 pm    Post subject:
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But why use a feature that is not yet obsolete, when one might expect it to become obsolete at some point?
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Anuj Dhawan

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PostPosted: Mon Sep 20, 2010 5:28 pm    Post subject:
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Actually, if I were to do what is asked - I could have used what Enrico has suggested. BUT...
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Phrzby Phil

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Location: Richmond, Virginia

PostPosted: Mon Sep 20, 2010 5:33 pm    Post subject:
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nareshkp's COBOL solution is fine, given the COBOL requirement.

But his caution about the record order shold be discarded in favor of writing the final 5 records out in the order in which they were received.

This is not too hard - just fill the table circularly and keep track of which position was last filled, then start writing from the following position, counting with mod5 arithmetic.
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Anuj Dhawan

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PostPosted: Mon Sep 20, 2010 5:35 pm    Post subject:
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Well, agreed. I gave just another altervative...
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dbzTHEdinosauer

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PostPosted: Mon Sep 20, 2010 5:54 pm    Post subject:
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this gets the job done without worrying about were/when/what

Code:

01  last-six-area.
    05  first-five       pic x(400).
    05  last-read        pic x(080).
01  last-six-hold-area
    redefines
    last-six-area.
    05  filler           pic x(080).
    05  last-five        pic x(400).
01  last-six-records
    redefines
    last-six-area.
    05  one-of-the-records pic x(080) occurs 6 times.

INITIALIZE last-six-area
OPEN input-file
Perform read-input
  until eof
CLOSE input-file
DISPLAY 'fourth from last ' one-of-the-records(1)
DISPLAY 'third  from last ' one-of-the-records(2)
DISPLAY 'second from last ' one-of-the-records(3)
DISPLAY 'first  from last ' one-of-the-records(4)
DISPLAY 'last             ' one-of-the-records(5)
GOBACK

READ-INPUT.
  move last-five  to first-five
  Read input-file-record into last-read
.
999-exit.
    exit.

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hamsalakshmi

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PostPosted: Tue Sep 21, 2010 1:15 pm    Post subject: Reply to: Option to pick last 5 records from flat file.
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Thanks to all for your suggestions........
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bhavin.mehta

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Joined: 25 Jun 2012
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PostPosted: Mon Jun 24, 2013 7:36 pm    Post subject:
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@dbzTHEdinosauer

I really like the way you code... icon_biggrin.gif
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