Export selected records to CSV using python (IDLE)

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03-22-2017 09:15 AM
TheoFaull
Occasional Contributor III

Hello all!

I have a polygon shapefile. It contains 200 records and a (long) field with reference numbers (type codes) 0, 1, 2 or 3.

I have a point shapefile with 25,000 records. The points fall inside the various polygons throughout the map.

I want to-

Select all points that intersect the polygons that have a type code of 0, and export this selection of points to a new CSV file.

Then repeat this process for ref number = 1, 2 and 3...

4 seperate scripts (one for each ref number) or 1 script doing it all at once: either would be fine.

I want to do all this using the IDLE python GUI rather than going into ArcMap. So I want the script to point to shapefiles on my hard drive raher than layers in the Table Of Contents.

I'm still a noob at python so all I have on my mind so far is:

# Import the required python modules (I still don't quite know what this does)

??? import arcpy ???

??? from arcpy import env ???

# set the workspace environment

??? env.workspace = "C:\Data\" ???

# Select all polygons where type code = 0 and export it to a temporary feature class

arcpy.Select_analysis('C:\Data\Polygon.shp', r'\\somernt\curo\users\faullt\ArcGIS\Default.gdb\Type_code_0_polygon', '"Type_code" = 0')

# select all points that intersect the new 'type code = 0' feature class

arcpy.SelectLayerByLocation_management('C:\Data\Points.shp', 'INTERSECT', 'Scheme- unknown or no restriction', '#', 'NEW_SELECTION', 'NOT_INVERT')

# export the new selection of points to a CSV file in C:\Data

??? ???

# display a completion message

print "CSV created"

The actual lines of python I have typed above are taken from dragging the results in the geoprocessing results pane into an ArcMap python window...

Any help would be much appreciated!

Thanks

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JamesCrandall
MVP Frequent Contributor

I'm typically using the numpy and pandas libraries and they have good export/saveas functionality. Just convert your Feature Class to a numpy array and then save it to csv.

import numpy
import pandas as pd
fc = r'H:\Documents\ArcGIS\Default.gdb\MyFeatureClass'
nparr = arcpy.da.FeatureClassToNumPyArray(fc,['Field1', 'Field2', 'Field3'])
pdarr = pd.DataFrame(nparr)

pdarr.to_csv(r'H:\nparr.csv')

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5 Replies
NeilAyres
MVP Frequent Contributor

You say :

The points fall inside the various polygons throughout the map

And

Select all points that intersect the polygons that have a type code of 0, and export this selection of points to a new CSV

So you are not doing a join here? No info from the polygons is joined to the points?

So why not just create 4 layers in your map using definition queries, then use the export to excel tool?

If you know nothing about scripting or python, this will be the simpler way.

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TheoFaull
Occasional Contributor III

No I don't want to join the datasets as I don't need any info from the polygon layer.

I just want a script that creates a CSV or Excel file of all points that fall within all the polygons where Type Code = 0 (and then 1, 2, 3)

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TheoFaull
Occasional Contributor III

I'm starting to believe I won't be able to do any of this without opening ArcMap, as the select by location tool can only deal with layer inputs from the Table of Contents, not shapefile inputs from a C drive location.

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JamesCrandall
MVP Frequent Contributor

I'm typically using the numpy and pandas libraries and they have good export/saveas functionality. Just convert your Feature Class to a numpy array and then save it to csv.

import numpy
import pandas as pd
fc = r'H:\Documents\ArcGIS\Default.gdb\MyFeatureClass'
nparr = arcpy.da.FeatureClassToNumPyArray(fc,['Field1', 'Field2', 'Field3'])
pdarr = pd.DataFrame(nparr)

pdarr.to_csv(r'H:\nparr.csv')

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DarrisFriend
Occasional Contributor

James Crandall‌ Excellent advice to use pandas and numpy. If saved me a lot of headache trying to make arcpy.TableToTable_conversion work in a certain out field order.

By the way for others that don't know you can exclude the index added to the front of each row using index=False 

pdarr.to_csv(fileName,header=False, index=False)

See also pandas.DataFrame.to_csv — pandas 0.23.3 documentation