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Best way to find a change of sign

  • July 13, 2017
  • 8 replies
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jdh
Contributor
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I have some ordered features that contain a value, and I need to identify the inflection points, ie the feature where the sign (+/-) of the attribute value changes compared to the previous feature

 

 

ex. features have values [2,3,1,-2,-1,1,3] the inflection points would be features 3 and 5

For added entertainment there is another attribute containing a common ID, and I need to break on that value.

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    8 replies

    erik_jan
    Contributor
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    • erik_janContributor
    • Contributor
    • July 13, 2017

    I will give it a try:

    Create a new attribute ABS with conditional value (if value = @abs(value) then Y else N).

    Then create the test between the current and the previous feature (ABS = ABS(feature(-1))

    That should list the changes in the Failed port of the Tester.

    jdh
    Contributor
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    • jdhContributor
    • Author
    • Contributor
    • July 13, 2017

    I will give it a try:

    Create a new attribute ABS with conditional value (if value = @abs(value) then Y else N).

    Then create the test between the current and the previous feature (ABS = ABS(feature(-1))

    That should list the changes in the Failed port of the Tester.

    I tried using an attributeCreator with the expression ((@Value(X)>=0)==(@Value(feature[-1].X)>=0)),

     

     

    But I'm not sure how to prevent the first feature from one group checking against the last feature of the previous group.
    erik_jan
    Contributor
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    • erik_janContributor
    • Contributor
    • July 13, 2017
    I tried using an attributeCreator with the expression ((@Value(X)>=0)==(@Value(feature[-1].X)>=0)),

     

     

    But I'm not sure how to prevent the first feature from one group checking against the last feature of the previous group.
    In my example I would add to the Tester:

     

    And group = group(feauture(-1))

     

     

    erik_jan
    Contributor
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    • erik_janContributor
    • Contributor
    • July 13, 2017
    I tried using an attributeCreator with the expression ((@Value(X)>=0)==(@Value(feature[-1].X)>=0)),

     

     

    But I'm not sure how to prevent the first feature from one group checking against the last feature of the previous group.
    Let me change that to:

     

    Or group != group(feature(-1))

     

    That will pass the first in each group.

     

     

    ebygomm
    Influencer
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    • ebygommInfluencer
    • Influencer
    • July 13, 2017

    Might need tweaking to handle first and last features but you probably want a conditional statement with a composite test

    e.g.

    takashi
    Celebrity
    • takashiCelebrity
    • July 14, 2017

    Hi @jdh, if I understood the requirement correctly, this should work as expected.

    [Addition] Assume that 0 won't occur in the values sequence.

    Why not inspect features with Visual/Data Preview and Feature/Record Information before writing them into a destination dataset?
    takashi
    Celebrity
    • takashiCelebrity
    • July 14, 2017

    Hi @jdh, if I understood the requirement correctly, this should work as expected.

    [Addition] Assume that 0 won't occur in the values sequence.

    0684Q00000ArLJhQAN.png

    If 0 could occur in the sequence and 0 can be considered as a positive value, this Test Condition might work a treat. 

     

    @Evaluate((@Value(feature[-1].value)==0 ? 1 : @Value(feature[-1].value)) * (@Value(value)==0 ? 1 : @Value(value))) < 0
    If you consider 0 as a negative value, replace "1" in the expression with a negative value e.g. "-1".
    Why not inspect features with Visual/Data Preview and Feature/Record Information before writing them into a destination dataset?
    jdh
    Contributor
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    • jdhContributor
    • Author
    • Contributor
    • July 14, 2017
    If 0 could occur in the sequence and 0 can be considered as a positive value, this Test Condition might work a treat. 

     

    @Evaluate((@Value(feature[-1].value)==0 ? 1 : @Value(feature[-1].value)) * (@Value(value)==0 ? 1 : @Value(value))) < 0
    If you consider 0 as a negative value, replace "1" in the expression with a negative value e.g. "-1".
    I believe we have to allow for 0 in the sequence, because the first feature has no prior feature and would use the default value of 0.   In that case it would ideally be neutral, so I think your first equation works as is.

     

     

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