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2e5257372b
Because certain aggregates and concatenation requires results in
a certain order, this change allows specific control of the order
features are added to the aggregate during an expression evaluation.
E.g.
concatenate("Station",concatenator:=',', order_by:="Station")
will give a comma separated list of station names in alphabetical
order, rather than layer feature order.
Sponsored by SMEC/SJ
18 lines
1.8 KiB
Plaintext
18 lines
1.8 KiB
Plaintext
{
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"name": "relation_aggregate",
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"type": "function",
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"description": "Returns an aggregate value calculated using all matching child features from a layer relation.",
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"arguments": [
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{"arg":"relation", "description":"a string, representing a relation ID"},
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{"arg":"aggregate", "description":"a string corresponding to the aggregate to calculate. Valid options are:<br /><ul><li>count</li><li>count_distinct</li><li>count_missing</li><li>min</li><li>max</li><li>sum</li><li>mean</li><li>median</li><li>stdev</li><li>stdevsample</li><li>range</li><li>minority</li><li>majority</li><li>q1: first quartile</li><li>q3: third quartile</li><li>iqr: inter quartile range</li><li>min_length: minimum string length</li><li>max_length: maximum string length</li><li>concatenate: join strings with a concatenator</li></ul>"},
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{"arg":"expression", "description":"sub expression or field name to aggregate"},
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{"arg":"concatenator", "optional":true, "description":"optional string to use to join values for 'concatenate' aggregate"},
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{"arg":"filter", "optional":true, "description":"optional filter expression to order the features used for calculating the aggregate. Fields and geometry are from the features on the joined layer."}
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],
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"examples": [
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{ "expression":"relation_aggregate(relation:='my_relation',aggregate:='mean',expression:=\"passengers\")", "returns":"mean value of all matching child features using the 'my_relation' relation"},
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{ "expression":"relation_aggregate('my_relation','sum', \"passengers\"/7)", "returns":"sum of the passengers field divided by 7 for all matching child features using the 'my_relation' relation"},
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{ "expression":"relation_aggregate('my_relation','concatenate', \"towns\", concatenator:=',')", "returns":"comma separated list of the towns field for all matching child features using the 'my_relation' relation"}
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]
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}
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