Re^2: Opening random files then reading random lines from file.

If I correctly understand the

rand($.) < 1 && ($line = $_) while <>
[download]

there is no need to know the number of the lines in the file.

Comment on Re^2: Opening random files then reading random lines from file. Download Code
Re^3: Opening random files then reading random lines from file. by brx (Pilgrim) on Apr 27, 2012 at 09:18 UTC
Yep. This idea is beautiful. First line: `$.== 1` => 1/1 chance to keep this line1. Second line: `$. == 2` => 1/2 chance to keep line2 (so 1-(1/2)=1/2 to keep line1) (Equiprobability) Third line: `$. == 3` => 1/3 chance to keep line3 ( so (1-(1/3))=2/3 chance to keep a previous line (line1 or line2) : (2/3)(1/2)=1/3 for line1 and same thing 1/3 for line2 (Equiprobability) (N+1)th line: `$. == N+1` => 1/(N+1)* chance to keep line(N+1) so (N+1 -1)/(N+1) to keep a previous line, one of all previous N lines (each one has 1/N): for each previous line probability is ((N+1 -1)/(N+1))(1/N) = 1/(N+1)* (Equiprobability again)	[reply] [d/l] [select]
Re^3: Opening random files then reading random lines from file. by rovf (Priest) on Apr 30, 2012 at 08:42 UTC
You are absolutely right; when I wrote my comment, I did not know yet the ingenious (and simple!) algorithm proposed by JavaFan. -- Ronald Fischer <ynnor@mm.st>	[reply] [d/l]


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