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20 lines
2.2 KiB
Plaintext
20 lines
2.2 KiB
Plaintext
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{
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"name": "aggregate",
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"type": "function",
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"description": "Returns an aggregate value calculated using features from another layer.",
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"arguments": [
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{"arg":"layer", "description":"a string, representing either a layer name or layer 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":"calculation", "description":"sub expression or field name to aggregate"},
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{"arg":"filter", "optional":true, "description":"optional filter expression to limit the features used for calculating the aggregate"},
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{"arg":"concatenator", "optional":true, "description":"optional string to use to join values for 'concatenate' aggregate"}
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],
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"examples": [
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{ "expression":"aggregate(layer:='rail_stations',aggregate:='sum',expression:=\"passengers\")", "returns":"sum of all values from the passengers field in the rail_stations layer"},
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{ "expression":"aggregate('rail_stations','sum', \"passengers\"/7)", "returns":"calculates a daily average of \"passengers\" by dividing the \"passengers\" field by 7 before summing the values"},
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{ "expression":"aggregate(layer:='rail_stations',aggregate:='sum',expression:=\"passengers\")", "returns":"sum of all values from the passengers field in the rail_stations layer"},
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{ "expression":"aggregate(layer:='rail_stations',calculation:='sum',expression:=\"passengers\",filter:=\"class\">3)", "returns":"sums up all values from the \"passengers\" field from features where the \"class\" attribute is greater than 3 only"},
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{ "expression":"aggregate(layer:='rail_stations',calculation:='concatenate', expression:=\"name\", concatenator:=',')", "returns":"comma separated list of the name field for all features in the rail_stations layer"}
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]
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}
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