[GIS] Prefixing multiple values within QGIS using the Field Calculator

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I have a column in my my attribute table that contains a series of individually numbered locations. I wish to prefix all of these numbers with a letter, this letter will be the same for each of the values. E.g. 100, 200 and 300 would become A100, A200 and A300. I have a lot of data so simply going through and renaming would take a lot of time.

I have a feeling this would be achieved through the Field Calculator but unsure of which expression would be best for this?

Best Answer

Simple solution:

'A' ||  "column name"

in a new field of type String.

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[GIS] QGIS field calculator expression: selecting min/max values within field groups

Well i want did the same but, i can´t find... this the way i solve it. Maybe can help to anybody

from qgis.core import *
import qgis.utils
canvas = qgis.utils.iface.mapCanvas();
layer = canvas.layer(1)

maxArea = 0
maxId = 0
selection =[]

uniquevalues = [];
dP= layer.dataProvider()
id = dP.fields().indexFromName('myColumn')
#i have the unique values from some column
uniquevalues = dP.uniqueValues( id )
#then i go for each value that is equal to my Unique value
for uv in uniquevalues:    
    exprec = QgsExpression( 'myColumn = ' + uv )
    exprec.prepare( layer.pendingFields() )
    for feature in layer.getFeatures():
        value = exprec.evaluate( feature )

        if bool( value ):
            #areaDegs is the column what i want get the max value
            if feature['areaDegs'] > maxArea :
                maxArea = feature['areaDegs'] 

                maxId = feature.id()
    #here i store de Id´s width de Max values and unique values from myColumn
    selection.append( maxId )
    maxId =0
    maxArea = 0
layer.setSelectedFeatures( selection )

Maybe there are a best way to do it, but for now, this is the way i do it.

Best Answer

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