Changing data type in attribute table in QGIS?

Question

I have county data in which the FIPs (actually State FIPS and County FIPS combined). I have data imported as CSV with the sames FIPS data titled STCounty. However, the shapefile FIPS is listed as a Real and the CSV came in as an Integer and the Join function does not seem to work. The drop boxes are greyed out/empty.

So the bigger questions is how do you change the attribute type in a table?

I tried to create a new column in the shapefile (county data) and set it to an integer and then multiply the FIPS*1, but got a column full of "NULL".

I am new to QGIS and have a lot of experience in MapInfo, so the join concept is not new to me, just the syntax in QGIS.

Answer 1

Creating a new integer column is the right way to go - but the 1*FIPS that you used (which would work in Excel or Libreoffice) is where the problem comes in; QGIS doesn't automatically convert between field types in a calculation.

You need to use one of the conversion functions (toint converts to integer, tostring to text, and toreal to real/decimal) with the correct column name:

toreal("FIPS")

You can use the Tablemanager plugin to then remove unnecessary columns.

Setting up a .csvt file would be the best repeatable solution but for a single column, this should be pretty straightforward.

Answer 2

I once answered this question;If you import your Data from a csv file you need to create a csvt file in order to determine the attribut type of a field. See the explanation here: Changing CSV layer attribute value from text to number in QGIS?

Jo

Answer 3

I just had the same problem. In my case i work with Libreoffice and QGIS.

I exported a table from R to .CSV with two columns: "id" and "veh". "id" is Integer and "veh" Real.

write.csv(tab2,file='/path/table.csv',row.names = F)

When i open the table.csv in Libreoffice the field veh was read it as "string". So i created another coulmn "vehh" as the multiplication of "veh"*1, and the result was the desired number . Then i saved the file as .ODS (Libre Office)

Then i load the table.ODS in qgis and "vehh" was recognized as Real.