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Extracting percent difference RRS feed

  • General discussion

  • I think you really want:

    $day1 = (dir $path |?{$_.LastWriteTime -gt [datetime]::Today.AddDays(-3) -and $_.LastWriteTime -lt [datetime]::Today.AddDays(-2)}).Count

    The math is:

    $day1/$day2 -gt .25


    \_(ツ)_/


    It was just a hint, not the solution.  :)

    Although i must admit, that using calculate property was not necessary there, so my example was not correct  (datetime comparison was right though)


    • Edited by Mekac Friday, October 19, 2018 7:46 AM
    • Split by jrv Friday, October 19, 2018 9:20 AM Discussion
    • Edited by jrv Friday, October 19, 2018 9:22 AM fixed
    • Moved by jrv Friday, October 19, 2018 9:27 AM broken thread context
    Friday, October 19, 2018 7:41 AM

All replies

  • But the hint doesn't work.  A hint should be workable.


    \_(ツ)_/

    Friday, October 19, 2018 7:42 AM
  • Well my hint did count the files using datetime criteria .. so it was workable in my point of view  (though your example is better).

    $day1/$day2 -gt .25 .. this doesnt either .. this doesn't give u required %

    Friday, October 19, 2018 7:53 AM
  • It gives the answer. If day2 is 25%greater than day1 the expression is rue.

     1/($day1/$day2) -1 gt .25  is the percentage as a decimal value.


    \_(ツ)_/




    • Edited by jrv Friday, October 19, 2018 9:00 AM
    Friday, October 19, 2018 7:57 AM
  • Oops.  My formual should be:

     1/($day1/$day2) -1 gt .25


    \_(ツ)_/




    • Edited by jrv Friday, October 19, 2018 9:00 AM
    Friday, October 19, 2018 7:58 AM
  • Oops.  My formual should be:

    1 - ($day1/$day2) -gt .25


    \_(ツ)_/


    So.. when 1 day is 50logs, second day is 70 logs..   then its .28  => your statement is correct.

    What about 1 day 70logs, second 50 logs..  then its -0.4, right? :)  Therefore your formula needs some more tweaking as were looking for 25% differency..   no matter if second day count Is higher or lower ..


    • Edited by Mekac Friday, October 19, 2018 8:17 AM
    Friday, October 19, 2018 8:16 AM
  • No.  You have to understand the mathematical concept of percent difference.  Greater than 25% more means day 2 is more than 1.25.

    Look at it this way.

    $day2/$day1 -gt 1.25

    which is probably a clearer way of stating the question.  The result of the left side is alwys greater than 1.25 when day 2 has more than 1.25 times as many files.

    note that

    $day2/$day1 -eq 1

    means that they are equal when it is true.

    Another way of saying this is:

    if $day2/$day1 is less than 0 or greater than then it is not equal.

    The following:

    $day2/$day1 -gt 1.25

    means that any time day 2 is more than 25% greater the expression is true.

    Logic.  It is what makes computers work.  It is a fundamental pattern in programming.

    This is all based on junior high school math so everyone should know it cold.  Right?

    Of course we can just invert this for more fun.

    $day1/$day2 -lt .75

    Which is the same test.

     1/($day1/$day2) -1 gt .25
    $day1/$day2 -lt .75
    $day2/$day1 -gt 1.25

    Are all the same test and are equivalent.  They al test for the same condition.


    \_(ツ)_/



    • Edited by jrv Friday, October 19, 2018 8:59 AM
    Friday, October 19, 2018 8:45 AM
  • Opps again.

    The correct formula should be

    1/($day1/$day2) -1

    Getting late and I forgot that little bit.


    \_(ツ)_/

    Friday, October 19, 2018 8:59 AM
  • I should explain.

     1/($day1/$day2)

    This gets the inverse of the ratio. 

     1/($day1/$day2) -1 gt .25

    subtract one to get the match to normalize at .25.

    When $day2 is greater than $day the result is always positive.  When $day1 is greater than 2 time $day2 the result is always negative.

    This is why this formula is easier to use and understand as well as its variation (-1).

    $day2/$day1 -gt 1.25

    Note that a percent is not a numeric type but are a convenience added for display and obtained by multiplying by 100 and adding %.


    \_(ツ)_/


    • Edited by jrv Friday, October 19, 2018 9:08 AM
    Friday, October 19, 2018 9:05 AM
  • Moving to OFF-TOPIC posts because split thread doesn't make much sense by itself.


    \_(ツ)_/

    Friday, October 19, 2018 9:26 AM