Geographic Information Systems Asked on August 9, 2021
I have a shapefile that contains building footprints with multiple addresses with different functions (with each an usable area).
I would like to calculate the sum of the usable area, per building id, per same function, as such:
id | function | area |
---|---|---|
1 | wo | 10 |
1 | wi | 2 |
2 | wo | 50 |
1 | wo | 10 |
↓ calculate sum (area) when same id and same function
id | function | area |
---|---|---|
1 | wo | 20 |
1 | wi | 2 |
2 | wo | 50 |
I tried to use the following expression:
sum(expression[,group_by][,filter])
But the group_by
is only possible once (for instance to group the id).
How can we calculate the sum of the two features only when these have the same id and same function?
There is also a possibility using a "Virtual Layer" through Layer > Add Layer > Add/Edit Virtual Layer...
Let's assume there is a point layer called "test"
with its attribute table, see image below.
With the following query, it is possible to calculate the sum of the features only when these have the same "id"
and the same "function"
, as well as getting rid of duplicates.
SELECT SUM(value) AS sumvalue,
COUNT(*) AS numgrouped,
"id"||"function" AS grouped,
geometry AS geom
FROM "test"
GROUP BY "id", "function"
The output point layer with a new attribute table will look like
Last but not the least, keep in mind that:
Correct answer by Taras on August 9, 2021
Use a combination of the two fields like concat: "id" || "function"
for the group_by
part of the expression:
sum("area","id"||"function")
Answered by Babel on August 9, 2021
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