QGIS select by expression based on different elements concatenated inside a string

Question

Using the field filter or advanced filter expression in the attribute table of QGIS, I want to select features that have values in the first three levels and exclude features that values other than zero in levels four and onward.

Using the example data below, I want to select A and B, but not C.

Example Attribute data (letters and brackets and '...' are not in attribute table):

A] 100-000025-000000-000000-000000-000000-000000...

B] 100-000061-136148-000000-000000-000000-000000...

C] 100-023788-278991-424721-236628-000000-000000...

The value is a 144 character string broken into 21 levels. The levels in the code represent the hierarchy of the stream network – a major river would have only Level 1 of the code populated, a stream flowing directly into a major river would have levels 1 and 2 populated, and a stream flowing into this stream would have levels 1, 2 and 3 populated, and so on.

Answer 1

Use Select by expression with this expression (explanation below:

array_sum(
    array_foreach (
        generate_series (0,3),
        string_to_array (levels, delimiter:='-')[@element]>0
    )
)=3

To select features with values>0 only in the first 2 levels (include first feature), change the expression to <=3 in the last line.

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Explanation: The expression turns the string to an array and checks for the first 4 (0 to 3) elements if it is >0. It then calculates the sum of the elements for which this is the case. Sum = 3 means: first three elements > 0.

Answer 2

Using the example data, if you want to select A and B but not C, the recommended expression is:

string_to_array (levels, delimiter:='-')[3]='000000'

the expression will select all the records that have level 4 equal to the string '000000' and therefore all the features with level 1, 2 and 3 different from '000000'