topic Re: Keeping statistics with multi-field dissolving in Data Management Questions

Keeping statistics with multi-field dissolving

JonasDanner — Fri, 24 Aug 2018 08:25:16 GMT

Hello,

I have a tram-track layer with many single segments I want to dissolve by multiple fields, e.g. by tramline-number and if its a single-track or double-track segment of the tram. So alle the single-track parts of line 1 as one feature, all double track parts of line 1 as another feature, single track for line 2, double track for line 2 and so on. Choosing both fields (line number and Track type) as dissolving fields works fine for aggregation (no multipart-features).

But not for the statistics. I also want to sum the number of signals along each new feature. so I used the "number of signals" field in my attribute table as a statistic field, type sum. But the result is the same number of signals for each part of line 1, so single track for line 1 --> 16 signals, double track for line 1 --> 16 signals. But there are 16 signals along the whole line 1, it should be single track for line 1 --> 6 signals, double track for line 1 --> 10 signals.

Does someone know how to fix this? (it's not only those two lines, so I can't do it manually...)

Thanks in advance

Jonas

Re: Keeping statistics with multi-field dissolving

DanPatterson_Retired — Sat, 25 Aug 2018 21:07:01 GMT

maybe showing some portions of the sample tables would help.

Are you trying to get this into one table or are you looking at how to efficiently set up a series of joins/relates?

Re: Keeping statistics with multi-field dissolving

JonasDanner — Mon, 03 Sep 2018 09:17:17 GMT

Sorry for the late reply, I was on holiday and only came back into office today. The data is held non-public, so I'm held to not publish it...

I was trying to get it into one table.

Dissolving it after multiple fields only worked with the segments, so indeed all the single track parts of line x and all the multi part tracks of line x as well as all the single track parts of line y and all the multi part tracks of line y and so on were aggregated as one part each. but the attribute table showed multi track for all of the 4 cases... And the calculated Statistics were only for one of the dissolving fileds, as mentioned above.

I don't know exactly what happened, but it seems the programm could't handle a dissolving process with 5 fields. But I could solve it with this workaround: creating a new field in the attribute table (text-type), calculated it as a comination of the 5 fields I wanted to dissolve after. Now I could use this field to dissolve after, and with only this one field all the statistics were calculated correctly!

Re: Keeping statistics with multi-field dissolving

DanPatterson_Retired — Mon, 03 Sep 2018 11:20:56 GMT

That would be the solution since it simplifies the dissolve to one case