Differences

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--- transformations:filter [2015/03/20 21:33] – elenap
+++ transformations:filter [2021/04/25 14:00] – craigt
@@ Line 1: / Line 1: @@
-===== Filter by Condition =====
+{{ transformations:ExpressionFilterAction.png}}
+====== FILTER BY CONDITION======
+Category: Transform / Filters\\
-This transformation calculates an [[syntax:start|expression]] for every row (without adding a new column) and leaves only rows where this expression is true. Other rows are removed.
+\\
+=====Description=====
+This action calculates an [[syntax:start|expression]] for every row (without adding a new column) and keeps only rows where this expression is TRUE. All other rows are removed.
-The expression should be logical and return a boolean value (i.e. either true or false).
+The expression must be a valid condition -- it must return either TRUE or FALSE for any row in the table. If it results in a non-boolean value (i.e. not TRUE or FALSE) for at least one row it will cause a project execution error.\\
-**Examples of conditions**
+\\
+=====Use cases=====
+Create subsets of a dataset based on values across multiple columns.
+Clean a dataset by removing records that don't meet certain criteria, or evaluate to a certain value. \\
+\\
+=====Action settings=====
+^Setting ^Description ^
+|Expression|Enter an expression that evaluates to a boolean TRUE/FALSE result.  The expression will be applied to each\\ record and remove records that do not meet the criteria (evaluate to FALSE).|
+\\
+=====Remarks=====
+**Examples of valid expressions:**
+<code>
   [Amount]=0
@@ Line 13: / Line 31: @@
   not isempty([Email])
+</code>
+If no rows satisfy the condition then all rows are removed.\\
+\\
+=====Examples=====
+**Objective:** Find all rivers that are longer than 6000 km.\\
+**Source table:** The longest rivers in the world
+^River  ^Length (km)  ^Continent  ^
+| Nile  |  6650| Africa  |
+| Amazon  |  6400| South America  |
+| Yangtze  |  6300| Asia  |
+| Mississippi  |  6275| North America  |
+| Yenisei  |  5539| Asia  |
+| Yellow River  |  5464| Asia  |
+| Ob  |  5410| Asia|
+| Paraná  |  4880| South America  |
+\\
+**Action parameters:**
+> Expression: [Length (km)] > 6000
+\\
+**Result:**
+^River  ^Length (km)  ^Continent  ^
+| Nile  |  6650| Africa  |
+| Amazon  |  6400| South America  |
+| Yangtze  |  6300| Asia  |
+| Mississippi  |  6275| North America  |
+\\
+=====See also=====
+  * [[transformations:selectionfilter|Filter]]
+  * [[transformations:searchfilter|Filter by search]]
+  * [[transformations:filterbytype|Filter by type]]
+  * [[syntax:start|Expressions:  Expression syntax]]
-If no rows satisfy the condition then all rows get removed.