Hfrhyu

I'm working on a function to perform operations on folders of vector files.

These files might have differing attribute fields but there will be a common field between them. I'm using fiona in python to do the work.

A section of code is attached below and I'm using meta = input.meta to gather all the information about the input file to write to the output file.

This is being designed to work on different vector files. So the common field may be different in each run. For example, it might be a string field in one instance or an integer in another.

Despite not knowing beforehand what type of field the input field would be, is it possible to only include the specified field in the output file?

Whilst keeping the other information, such as projection and geometry type, the same as the input.

for file in veclist:
 with fiona.open(file) as input:
 meta = input.meta
 outfilename = os.path.join(outdir, os.path.basename(file).replace('.shp', "_d.shp"))
 with fiona.open(outfilename, 'w', **meta) as output:

I've tried to edit the dictionary of the schema and I've had some success

for file in veclist:
 with fiona.open(file) as input:

 fieldvalue = input.schema['properties'][target_field]

 input.schema['properties'].clear()

 input.schema['properties'][target_field] = fieldvalue

 meta = input.meta
 outfilename = os.path.join(outdir, os.path.basename(file).replace('.shp', "_d.shp"))
 with fiona.open(outfilename, 'w', **meta) as output:

As print(input.schema) listed this:

'geometry': 'Polygon', 'properties': OrderedDict([('Field_Name', 'str:254')])

And print(input.meta) listed this:

'crs': u'lon_0': -2, u'k': 0.9996012717, u'datum': u'OSGB36', u'y_0': -100000, u'no_defs': True, u'proj': u'tmerc', u'x_0': 400000, u'units': u'm', u'lat_0': 49, 'driver': u'ESRI Shapefile', 'crs_wkt': u'PROJCS["OSGB_1936_British_National_Grid",GEOGCS["GCS_OSGB 1936",DATUM["OSGB_1936",SPHEROID["Airy_1830",6377563.396,299.3249646]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",49],PARAMETER["central_meridian",-2],PARAMETER["scale_factor",0.9996012717],PARAMETER["false_easting",400000],PARAMETER["false_northing",-100000],UNIT["Meter",1]]', 'schema': 'geometry': 'Polygon', 'properties': OrderedDict([('Field_Name', 'str:254')])

But I get this error on trying to write the shapefile:

 File "/.local/lib/python2.7/site-packages/fiona/collection.py", line 355, in write
 self.writerecords([record])
 File "/.local/lib/python2.7/site-packages/fiona/collection.py", line 349, in writerecords
 self.session.writerecs(records, self)
 File "fiona/ogrext.pyx", line 1168, in fiona.ogrext.WritingSession.writerecs
ValueError: Record does not match collection schema: [u'Field_Name', u'pH', u'P_PPM', u'P_Index', u'K_PPM', u'K_Index', u'Mg_PPM', u'Mg_Index', u'2018_y_t_h', u'Grid_ID'] != ['Field_Name']

I thought I had successfully changed my schema and meta when I printed out the results. But it still seems to have picked up the original.