Re^2: Get unique fields from file

in reply to Re: Get unique fields from file
in thread Get unique fields from file

I do like this general approach, however the OP is talking about a significant sized file of 500 MB. Depending upon the data of course, your HoH (hash of hash) structure could consume quite a bit more memory than the actual file size in MB.

{
  head1 => { val1 => 2, val2 => 1, val3 => 1, val6 => 1 },
  head2 => { val2 => 1, val4 => 2, val7 => 2 },
  head3 => { val3 => 2, val5 => 3 },
}
[download]

I came up with a representation (at this post) where the column values only occur once as hash keys and the value of each hash key is an array describing whether a value: appears or doesn't appear at all in column, whether a value only appears once in a column, whether a value occurs more than once in a column.

We both interpreted "unique" to mean different things.
I see you think that means: "don't repeat yourself after having said something once".
I thought it meant: "don't say anything at all if you would repeat yourself".

My data structure:

{
  val1 => [-1],   # val1 occurs more than once in col 1
  val2 => [2, 1], # val2 occurs once in col 1 and once in col 2
  val3 => [-3, 1], #val3 occurs more than once in col 3
                   #but only one time in col1
  val4 => [-2],
  val5 => [-3],
  val6 => [1],
  val7 => [-2], #val7 is mentioned at least twice in col2
}
[download]

Of course I could generate your same output from my data structure because I know the columns where the term appeared more than once.

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Re^3: Get unique fields from file by LanX (Saint) on Jan 08, 2022 at 15:27 UTC
> Depending upon the data of course, your HoH (hash of hash) structure could consume quite a bit more memory than the actual file size in MB. This shouldn't be a problem if you a apply a sliding window technique° plus splitting the hashes into easily swappable chunks². The trick is to balance time, space and disk access, by minimizing the the number of swaps. This will scale well, until the limit given by disk-space. Cheers Rolf _{(addicted to the Perl Programming Language :) Wikisyntax for the Monastery} °) see Re: Memory Leak when slurping files in a loop (sliding window explained) ²) see Re: write hash to disk after memory limit Re: Small Hash a Gateway to Large Hash?	[reply]
Re^3: Get unique fields from file by tybalt89 (Monsignor) on Jan 07, 2022 at 04:49 UTC
Yep. I couldn't tell if what was wanted was "unique in row", "unique in column" or "only singletons in column", so I just thought I'd toss something out there. I do have a solution that takes practically no memory (uses external sort -u), but I'll wait to see responses to the proposed answers first.	[reply]
Re^4: Get unique fields from file by Marshall (Canon) on Jan 07, 2022 at 10:33 UTC
I see that we both had the same interpretation issue... As far as `sort -u` goes, I didn't know if the OP is on Windows, Unix or other platform. There is supposed to be an undocumented sort switch on Win10: `sort /UNIQ`, but I didn't bother to test that. This can be done in another way in the new PowerShell, but I didn't worry about that either. I also circled back to "what the heck does unique mean?".	[reply] [d/l] [select]

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