[Qgis-user] Edit attribute table rows

[Lester Anderson]

Hi Andreas,

Still having issues. I can see the logic of the CASE WHEN END, but I
am wondering if the problem is because "Depth" has both a NULL value
and a real value. I have tried all sorts of variants and cannot get
the NULL depth changed.

Attributes: strike dip rake magnitude quadrant depth
0 null null null null null "Tensional and compressional" null
1 233 38 -96 6.77 Compressional 623

So scanning for Depth=NULL is fine; this is actually all of the event
solutions, where the row with the values defines the nodal planes. I
have around 2928 events in the shapefile!

Can this be solved by scanning for the quadrant attribute, but then
how does one specify the value for "Depth". I think if one applies
"Depth" NOT NULL it returns 1

I could not find a guide in the documentation for the field calculator
that was similar.

Cheers
Lester

On 8 April 2016 at 15:00, Neumann, Andreas <a.neumann at carto.net> wrote:
> Hi Lester,
>
> The field calculator is meant to change "a lot" of values. It will update
> all selected records with the new value or calculation (expression).
>
> With CASE WHEN END you can introduce switches for different rules.
>
> So - please don't export to Excel. You can do it all with the field
> calculator.
>
> Andreas
>
> On 2016-04-08 15:28, Lester Anderson wrote:
>
> Hi Andreas,
>
> I am trying change a lot of values, if it was a few that is no problem.
>
> The other option is to export the attribute table as a database and
> edit in Excel etc and then join the table in QGIS
>
> Cheers
> Lester
>
> On 8 April 2016 at 14:23, Neumann, Andreas <a.neumann at carto.net> wrote:
>
> Hi Lester,
>
> I thought you want to set the value to 623 where the value was NULL before?
> - so just write 623 in the left field after you selected the values.
>
> Alternatively, you can do without the previous selection and use the
> following expression.
>
> CASE WHEN depth IS NULL THEN 623 ELSE depth END
>
> Hope this helps,
>
> Andreas
>
>
>
> On 2016-04-08 15:13, Lester Anderson wrote:
>
> Hello Andreas,
>
> Selecting the rows where depth = NULL is fine. The field calculator
> does not update the depth with the depth where known values are
> present.
>
> Only update selected features is checked, update existing field
> checked, with output field set to depth:
> Expression: tried just "depth" and also "depth"="depth".
>
> Have I missed something here?
>
> Thanks
>
> On 8 April 2016 at 12:30, Neumann, Andreas <a.neumann at carto.net> wrote:
>
> Sure.
>
> It is a two-step thing:
>
> 1. Select all records where Depth IS NULL. Use the "Select Features using an
> expression" button (the Epsilon sign) for that and "depth IS NULL" as an
> expression
>
> 2. Use the field calculator and only update the selected records (the top
> checkbox in the field calculator).
>
> You can find details about the field calculator in the QGIS manual.
>
> Hope this helps,
>
> Andreas
>
> On 2016-04-08 13:18, Lester Anderson wrote:
>
> Hello,
>
> I have an attribute table of earthquake data (focal mechanism beach
> balls) and need to edit the depth attribute. Each ball is defined by
> two rows in the table, eg first ball
>
> Row_ID Strike Dip Rake Magnitude Quadrant Depth
> ----------------------------------------------------------
> 0 NULL NULL NULL NULL Tensional and Compressional NULL
> 1 233 38 -96 6.77 Compressional 623
> 2 NULL NULL NULL NULL Tensional and Compressional NULL
> 3 68 36 83 5.7 Compressional 39
> etc
>
> where rows 0,1 and 2,3 represent separate beach balls, so basically it
> is a row calculation
>
> What I need to do is replace the Depth NULL value with the depth 623
> etc for each entry. Is there an easy way of doing this?
>
> Thanks
>
> Lester
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