Differences

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--- transformations:filter [2015/04/10 11:29] – elenap
+++ transformations:filter [2015/06/12 21:20] – dmitry
@@ Line 3: / Line 3: @@
 This transformation calculates an [[syntax:start|expression]] for every row (without adding a new column) and keeps only rows where this expression is true. 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**
@@ Line 15: / Line 15: @@
-If no rows satisfy the condition then all rows get removed.
+If no rows satisfy the condition then all rows are removed.
 **Example of transformation**
@@ Line 49: / Line 49: @@
 === See also ===
   * [[transformations:selectionfilter|Filter]]
+  * [[syntax:start|Expression syntax]]
+  * [[syntax:errorpropagation|Error propagation in expressions]]