5

I'll try to calculate the minimum value of four different columns in my QGIS table like:

enter image description here

The min. value would be 1,50286 in the first row.

Is there any expression or tool to find the minimum value and write it into a new field?

  • Please create a real table, or provide a screenshot, because currently 1 would be the min. value. – Erik May 21 at 10:58
9

Simply use Field Calculator and create new field with

min(A,B,C)

where A, B, C, are field names

enter image description here

If you need to keep the field (min_ABC) updated, set the expression to default value of the field. It can be done in Attributes Form setting in Layer Properties. Scroll down in the right part of window fill the default value and check Apply default value on update. Than it will automatically update when you change the values, and also works on new features.

enter image description here

Notice that this will work only on update not if you fill the values in the process of creating feature.

enter image description here

  • Just a small extension, in case, if you need to find a min value within all values (not only for a row/column), then just use minimum(min(A,B,C)) – Taras May 23 at 5:13
1

Tested on QGIS 2.18 and QGIS 3.4

In case if you do not want to modify your original data than I can suggest using a "Virtual Layer" through Layer > Add Layer > Add/Edit Virtual Layer...

Let's assume we have three features in "layer" with three values accordingly, see image below.

input

With the following Query, it is possible to achieve the result

SELECT l.*, MIN(l.Value1, l.Value2, l.Value3) AS MIN_VALUE
FROM layer AS l
GROUP BY l.id

The output Virtual Layer will maintain initial attributes and geometries and additional field 'MIN_VALUE'.

Output

  • 1
    Good suggestion, but keep in mind that virtual field is stored in the project not in the data. You can export the data, than the virtual field is converted to "non-virtual". – Oto Kaláb May 23 at 7:44
  • Truly agree with you. Thank you for a hint – Taras May 23 at 7:45

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