attribute-indexattribute-tablefield-calculatorqgis
I make a new column in my attribute table and it has a default value (for example 0). I want to (probably using the Field Calculator) have the result that row 1 has the value 1, row 2=2 and so on, just like a numbered index.
I'd be thankful for a code example for the field calculator (including the use of $rownum (I think I need this for switching to the line)).
Here's a funny trick using a Spatialite query to get the values in descending order. If you do a count() and use a WHERE clause to get values >= the current value, then you'll actually be getting the order, so if I have a table "mypoints" with a column "value" and an empty column of "value_order" then:
SELECT value, (
SELECT count(*) FROM mypoints AS my
WHERE my.value>=mypoints.value) AS orders
FROM mypoints
ORDER BY value DESC;
gives a list of the values and their order. I can then update the "value_order" column like so:
UPDATE mypoints SET val_order = (
SELECT count(*) FROM mypoints AS my
WHERE my.value>=mypoints.value
);
HTH
You can use regexp_match function to find starting position of the word within the string. Than with using condition if you can test if there is string occurence (e.g. starting position > 0) and set the value for TRUE (your value) and FALSE (0).
It should look like this:
if(regexp_match(taxa, 'Calluna_vulgaris')>0,1,0) +
if(regexp_match(taxa, 'Porpidia_crustulata')>0,2,0) +
if(regexp_match(taxa, 'Rhizocarpon reductum')>0,2,0) +
if(regexp_match(taxa, 'Micarea_erratica')>0,2,0)
Maybe there is better regexp solution, but I'm not so regexp ninja.
Best Answer
Just put
$rownum(QGIS 2) or@row_number(QGIS 3+) as the expression. Simple as that. :)An up-to-date list of all the field calculator functions can be read in the official docs.