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image_expression_null_value_handling [2022/08/22 03:38] admin [Proper Way of Testing for Image Values -- Guarding Against Null Values] |
image_expression_null_value_handling [2022/08/22 04:54] (current) admin [Null Evaluation] |
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| - | If you need to retrieve the number corresponding to a image null value, you can use the ''null( iX )'' expression. For instance, ''null(i1)'' returns the number corresponding to the null value of image ''i1''. So if, so some reason, you need to retrieve the image value or its corresponding numeric null value, you can use ''i1 ? null(i1)'' or ''if isnull(i1) then null(i1) then i1''. Note that ''null(i1)'' is very different from expression ''null'', since ''null(i1)'' always returns a valid numeric value and ''null'' returns a special construct that, if not contained, invalidates the expression evaluation producing null as a result. | + | If you need to retrieve the number corresponding to an image null value, you can use the ''null( iX )'' expression. For instance, ''null(i1)'' returns the number corresponding to the null value of image ''i1''. So if, so some reason, you need to retrieve the image value or its corresponding numeric null value, you can use ''i1 ? null(i1)'' or ''if isnull(i1) then null(i1) then i1''. Note that ''null(i1)'' is very different from expression ''null'', since ''null(i1)'' always returns a valid numeric value and ''null'' returns a special construct that, if not contained, invalidates the expression evaluation producing null as a result. |
| ===== Proper Way of Testing for Image Values -- Guarding Against Null Values ===== | ===== Proper Way of Testing for Image Values -- Guarding Against Null Values ===== | ||