I have a field called "Species" which is composed by two words (e.g. 'Robinia pseudoacacia') and I would like to extract the first letter of both the words in order to get two letters (e.g. 'Rp') in the label.
There other word pairs in the field "Species" so I guess it needs a rule which specifies that the extraction must be done for the first word (e.g. substr("Species", 1, 1)) as well as for the first letter after the space.
Here's a Regular Expression method, assuming you're doing this in the QGIS Field Calculator:
regexp_substr("yourfield",'\\w{1}') || regexp_substr("yourfield",' (\\w){1}')
\\w{1} -> get the 1st word 1st character and return. ` (\\w){1}` -> find a space, followed by a word character (record it) that appears exactly once and return the capture group (i.e. the 1 letter only, without the space)
You can achieve this in a single expression, that would work with any number of words
regexp_replace(field_name,'(^| )(\\w{1})[^ ]*','\\2')
First, let's note that we are using regexp_replace to remove any char but the 1st of each word. If we use regexp_substr, the search would stop at the 1st found occurence.
Let's break it down: Anything between parenthesis is a capture group, which is numbered starting at 1.
(^| ): the start of a string, or a space
(\\w{1}): followed by any word character, exactly once. --> this is the 1st letter of each word.
[^ ]*: followed by any number (*) of character that is not (^) a space
\\2: replace everything from above with the 2nd capture group, i.e. the 1st letter of each word
PS: word beginning detection can certainly be improved with a bit more regex kungfu..
.[^ ] - strips out two characters which works in your test example but not longer strings. You are missing a + at the end to capture additional non-space characters.
Commented
Dec 14, 2021 at 0:56
regexp_replace(field_name,'(^|\\W)+(\\w{1})[^\\s]+','\\2') Would need more tweaking for hybrid binomials e.g. Platanus x acerifolia.
Commented
Dec 14, 2021 at 1:01
[^ ]*, which would keep 1 letter word, and is nicely enhanced with your expression that removes it
Split string into an array by whitespace, pick first/last element, pick first letter, concat together:
concat(
substr(array_first(string_to_array( "scientificname", ' ')), 1, 1),
substr(array_last(string_to_array( "scientificname", ' ')), 1, 1)
)
Another idea is to use this expression:
array_to_string(
array_foreach(
string_to_array("test", ' '), regexp_substr(@element, '^[[:alpha:]]|[0-9]')
),
' ')
It employs the following functions: array_to_string(), array_foreach(), string_to_array(), and regexp_substr()
