QGIS: Labelling with parts of an attribute consisting of two or more words

Question

Working in QGIS, I have an attribute consisting of scientific names of species. I would like to label the points on the map with the first 3 left letters of both parts of the binominal scientific name.

If I could make those letters uppercase, it would be even more awesome. For example:

FRICOE
EPIBUG
MEGMAC
ACRUNG

I cannot create fields as it is a PostgreSQL database.

Answer 1

Use this expression in the Single Labels value:

with_variable('strings',
    string_to_array(replace(upper("taxon"),' ',',')),
    left(array_get(@strings,0),3) || left(array_get(@strings,1),3))

It generates a string, replacing spaces by commas in your "taxon" field and transforming it to all caps along the way.

Then this string is converted to an array of substrings (getting rid of the commas)

From this, the first 3 left characters of substring 0 and 1 are concatenated

Answer 2

You can use the following expression in the label engine to get the desired output:

concat(
    substr(
        string_to_array(
            upper("FieldName"), 
        ' ')[0],
    1,3),
    substr(
        string_to_array(
            upper("FieldName"),' ' 
        )[1],
    1,3)
)

You need to change the "FieldName" with the name of the field that you want to use in the expression above, "taxon" in your case.

Output: