Beefy Boxes and Bandwidth Generously Provided by pair Networks
No such thing as a small change

Re: grabbing random n rows from a file

by swkronenfeld (Hermit)
on Jul 18, 2006 at 21:53 UTC ( #562144=note: print w/replies, xml ) Need Help??

in reply to grabbing random n rows from a file

Does j change for each set, or do you want to print the same number of lines for each set? It sounds like the amount of lines for each set is the same. Assuming that you want to print the same amount of lines for each set, than do the following

-read an entire set, let $m = the number of lines read
-let $j = int(rand($m))+1
-print out $j lines of the first set that you've already read
-now read the file line by line, buffering the input, and after you've read out $m lines, print out the first $j lines for each set, and throw away the remaining ($m-$j) lines. j random lines from each set. Then you can throw away your buffer and start over.

As for the size of the file, just don't slurp the entire file into memory, read it line by line.

Have I answered your question? I have a feeling that I'm oversimplifying it. If so, please give a few more details.


Log In?

What's my password?
Create A New User
Domain Nodelet?
Node Status?
node history
Node Type: note [id://562144]
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others having an uproarious good time at the Monastery: (3)
As of 2022-08-18 05:48 GMT
Find Nodes?
    Voting Booth?

    No recent polls found