In a QGIS composer, I would like to add a text label with the calculation of % of length of the total layer with a specific feature value.
My layer is composed of roads lines and I would like to know the proportion of the total length which have a specific value, like 'good' for the "ROADCONDITION" field.
For another question I had a good answer for count function:
'Existing roads: ' || round(aggregate('releve_terrain','count', ' ',"ROADEXIS" = 'Yes') / layer_property('releve_terrain','feature_count') *100) || '%'
I am looking for some help to use another function.