Question

ExpressionEvaluator: How to extract a value out of a List-Attribut which has different List-numbers?

  • 28 July 2021
  • 7 replies
  • 95 views
S
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With this Expression I get the max-value of the 5 first List-values.

@max(@Value(FID{0}.FID),@Value(FID{1}.FID),@Value(FID{2}.FID),@Value(FID{3}.FID),@Value(FID{4}.FID))

 

But the features have different List-Numbers. Some of them 5, some of them more than 5. Is there a way to express not hard-coded? Where the Number of List-entries can be dynamic?

 

My solution to get the maximum value was the Listsorter. But I wonder, if there is a way with the ExpressionEvaluator. An expression which is not hard-coded seems to be very powerfull.

Thanks for help!

7 replies

alexlynch3450
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Did you only want statistics from list? use ListSummer.

or did you want to find the max 'elements' contained in list? use ListElementCounter

or did you want to find a value and return index of value? use ListSearcher and AttributeCreator -= _list{@Value(_list_index)}

 

alexlynch3450
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Did you only want statistics from list? use ListSummer.

or did you want to find the max 'elements' contained in list? use ListElementCounter

or did you want to find a value and return index of value? use ListSearcher and AttributeCreator -= _list{@Value(_list_index)}

 

you can also combine listsorter and listelementcounter to grab feature's last known index feature.

S
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FID_ModelNameIn this case I was looking for the maximum value in the list (not the maximum index, the maximum value). I know you can get that with the Listsorter. The same result you get with the ExressionEvaluator and the expression: 

@max(@Value(FID{0}.FID),@Value(FID{1}.FID),@Value(FID{2}.FID),@Value(FID{3}.FID),@Value(FID{4}.FID))

With this expression, you test only the values from five list-item(index 0 to 4).  

I wonder now, if there is a possibility to make an expression with a variable number of list-item.

 

In the picture you see the values from the attribut model_name, which I use for group by. With the FID I make a list. Out of this list I want to take the maximum FID.

alexlynch3450
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why don't you explode list, and run it through StatisticsCalculator- enable group processing @Value(MODEL_NAME)?

geomancer
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Userlevel 4
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The ListSorter transformer, with sorting order set to Descending, will put the highest value in item 0. Next you can extract the value of item 0 with the ListIndexer transformer.

If you don't want to sort your list, you can make a copy of it with the ListCopier transformer, and use the copy for sorting and extracting.

 

Edit: Ah, re-reading your question I now realise you already know how to use the ListSorter

geomancer
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Userlevel 4
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Even more simple: the ListRangeExtractor transformer extracts the minimum and maximum values from a list.

But this is still a solution that does not use the ExpressionEvaluator from your initial question.

Unfortunately something like @max(@Value(_list{}.MyValues)) does not work.

S
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ok, thank's for answering. anyway, it seems with list-elements it's not the idea to work with the expression evaluator.

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