QGIS – How to Perform Find and Replace in QGIS Field Calculator

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I'm trying to replace selected string values in an attribute table, eg. "Text1" for "Text2" (QGIS 1.8.0), patriculary for those rows with NULL values. I have been trying to use the replace expression (and any other that I have found) with no luck.

Are there any wildcard characters that I may be able to use in future?

Best Answer

You could try a case when expression:

case when "Column_1" is NULL then  replace("Column_2",'Text2','Text1') else "Column_2" end

Using the 'or' expression, you can add multiple columns with NULL-values to the code.

case when "Column_1" is NULL or "Column_3" is NULL then  replace("Column_2",'Text2','Text1') else "Column_2" end

edit:

If you want to replace NULL, forget the replace-expression (it only works for strings and NULL is no string). Try this exact code:

case when "Feature" is NULL then '12_1' else "Feature" end

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[GIS] remove whitespace Python code results in odd character – Field Calculator

My co-worker came up with this ArcPy script that fixed the problem...it did require making a new field:

arcpy.AddField_management(featureClass, 'MainStreet', 'TEXT')

sCursor = arcpy.SearchCursor(featureClass)
for sRow in sCursor:
    OID = sRow.OBJECTID
    name = sRow.MainSt.encode('ascii', 'ignore')

    query = '"OBJECTID" = ' + str(OID)
    uCursor = arcpy.UpdateCursor(featureClass, query)
    for uRow in uCursor:
        uRow.MainStreet = name
        uCursor.updateRow(uRow)

[GIS] Calculating row in field based off another row in same field using ArcGIS Field Calculator

Something like this should work - Finds all the values in Field1 and Field2 and stores them in a dictionary, then looks up that dictionary for the values to calculate the field.

You will need to update "Field1" and "Field2" in the cursor with your actual field names, and "MyFC" with the name of your layer.

Pre-Logic Script:

myDict = {}
with arcpy.da.SearchCursor("MyFC", ["Field1", "Field2"]) as cursor:
  for row in cursor:
    if row[1] and row[0] not in myDict:
      myDict[row[0]] = row[1]

def Calc( field1 , field2 ):
  global myDict
  if not field2:
    x = myDict[field1]
  else:
    x = field2
  return x

Field2=

Calc( !Field1! , !Field2! )

Best Answer

Related Solutions

[GIS] remove whitespace Python code results in odd character – Field Calculator

[GIS] Calculating row in field based off another row in same field using ArcGIS Field Calculator

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