Geographic Information Systems Asked on November 1, 2021
I have a problem.
I am digitizing the map and I want to distinguish one group of polygons from the other group.
The basic difference between them lies in their ID (string). One of them has the ID starting from SE-1-… and the other ones start from SE-2-…
I found some hints here:
How to select features containing specific text string using an expression in QGIS
which unfortunately doesn’t work in my example.
Once I write down the function, next press the "Add" (plus) button I am getting the box allocated for "All other values".
Is there any way to separate these 2 groups by this part of the string?
Categorizing by ID doesn’t make sense, because all polygon get their unique color, which makes a terrible mess.
UPDATE:
Function is not valid, the details are in the box below:
TITLE
FieldThe expression substr("TITLE", 4, 1)
returns the fourth character of the string. If the TITLE
field is consistently formatted, this will correspond to the particular category, either 1 or 2. Just enter that expression and click classify.
Alternatively, you could modify substr
's starting position and length, or if the SE-# is always at the beginning, simply use left("TITLE", 4)
to get the SE-# text, not just the number.
TITLE
FieldIf the SE-# text does not consistently appear at the beginning of the string, you can use the regex_substr
function. This is easiest for grabbing the entire SE-# text, but can be modified to grab just the number, or you can nest it within a right
function instead.
regexp_substr("TITLE", 'SE-[1,2]')
Answered by JoshC on November 1, 2021
Have you tried Conditional expressions like IF or CASE? Something like if( "TITLE" = 'SE-1' , 1, 0 )
Answered by Nelson Silva on November 1, 2021
In addition to Cyrmel:
The formula is "TITLE" LIKE '%SE-2%'
and than you have to classify (to 1/0 or true/false). If you want, you can also change manually the 0 and 1 in the legend.
Answered by Christophe P. on November 1, 2021
You did not specify the value which triggers whether your polygon should go into the first group or not - "TITLE" LIKE %SE-2%
returns 1 for true and 0 for false. instead of "all other Values", set one colour to 1 and one to 0.
Answered by Cyrmel on November 1, 2021
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