Calculate total area of features in different categories in attribute table QGIS

Question

I have a vector layer which includes the acreage of the different features, I want to calculate the sum acreage of all polygons with

Parcel size >400 acres
Parcel size <100acres
Parcel size >100acres
Parcel size > 1000acres

Answer 1

You can categorise your features using a field calculator expression such as this (in this case the output field is called size_range):

case 
    when acres <= 100 then 'lte_100'
    when acres > 100 and acres <= 400 then 'gt_100_and_lte_400'
    when acres > 400 and acres <= 1000 then 'gt_400_and_lte_1000'
    when acres > 1000 then 'gt_1000'
end

And then use the Statistics by categories tool:

Answer 2

Solution: array aggregate

Use aggregate function array_agg() with a filter, where area is the attribute field where the parcel size of each polygon is stored:

array_sum (array_agg (area, filter:="area" < 100))

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Advanced: all four values at once

To get all four values at once as an array, use this expression:

array_foreach(
    array ('<100','>100','>400','>1000'),
    eval ('array_sum (array_agg (area, filter:= area' || @element  || '))')
)

The expression, added with a round() function, shows the four sums in the preview: