Replacing all "NULL" values in multiple rows with "0"

Question

I am looking for a way to replace all "NULL"-Values throughout multiple rows/ all "NULL"-Values in an attribute table. The table is from a SHP-File (shapefile).

Is there any easy way? Right now I am selecting then by hand and replace them row by row which takes quite some time. I have already tried to look up a solution, however as I want to replace them in the whole table it seems to be not that easy.

Sorry, yes it is QGIS. Datasource is a Shapefile/ .SHP (i have merged multiple shape files into one). thanks a lot — Corninski, Oct 22 '20 at 14:34
How many columns exist in your database? What value(s) will replace the NULLS? For a given column, will that new value be the same, or different for every record in the database? Will the new value be the same, or different, for every column in your database? — Stu Smith, Oct 22 '20 at 15:19
https://gis.stackexchange.com/questions/79627/replacing-all-null-values-from-attribute-table-with-zeros-using-qgis — Christophe P., Oct 23 '20 at 12:43
Please, do not forget about "What should I do when someone answers my question?" — Taras, Jan 20 '22 at 11:54

BERA · Answer 1 · 2020-11-03T17:12:50.137

3

This should work with text and numeric fields. Backup your data first..

layer = QgsProject.instance().mapLayersByName('replacenulls_backup')[0]
fs = layer.fields()
d = {e:0 if f.isNumeric() else '0' for e,f in enumerate(fs)}
with edit(layer):
    for row in layer.getFeatures():
        data = row.attributes()
        for i, val in enumerate(data):
            if val == NULL:
                data[i]=d[i]
        row.setAttributes(data)
        layer.updateFeature(row)

edited Nov 03 '20 at 17:12

answered Oct 22 '20 at 16:58

BERA

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I had to replace fs=lyr.fields() with fs=layer.fields() but it did just what I needed. Very nice. As suggested have a backup since it changed the attributes in the layer instead of creating a new in memory layer or it gave me an AssertionError if I put the layer in an edit session before running. – John Nov 03 '20 at 15:45
@BERA, can you be so kind and criticize the code I wrote. Can you please give me a suggestion or a recommendation on how to make it better. Thank you. – Taras Nov 30 '20 at 09:24
1

I'm no expert on pyqgis. If it is working and is understandable it's good :). I thought assigning string fields with 0 and not '0' would cause errors but apparently not. You could replace the start/stop editing with a with edit(lines_null): – BERA Dec 01 '20 at 08:57

Taras · Answer 2 · 2021-05-03T07:15:36.210

1

A solutions with no programming required.

Let's assume there is a polyline layer 'line' (blue) with its attribute table accordingly, see image below.

Deploy the "Refactor fields" geoalgorithm. Unfortunately it has a disadvantage, filling the 'Source expression' with a Conditional Function is still necessary, i.e.

if(condition,result_when_true,result_when_false)

and get the output

edited May 03 '21 at 07:15

answered Oct 23 '20 at 13:20

Taras

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Replacing all "NULL" values in multiple rows with "0"

2 Answers2