Spatial Join’s hidden trick on how to transfer attribute values in a One to Many relationship

[#1]

There is this  awesome blog by Esri Australia regarding joining multiple features to one feature:

https://esriaustraliatechblog.wordpress.com/2015/06/22/spatial-joins-hidden-trick-or-how-to-transfer...

There is also official Esri documentation on this procedure as well:

“Merge rules > Join
A concatenation of input field values. You can use a delimiter to separate the various input values. If no delimiter is used, all values will be joined into one continuous string.”

Analyze > Executing tools > Executing tools using the tool dialog > Special parameter controls:
https://desktop.arcgis.com/en/arcmap/latest/analyze/executing-tools/using-the-field-mapping-control....

Looks like this is also possible with arcpy.SpatialJoin_analysis python tool:
Analyze > Python > Working with sets of data in Python:
https://desktop.arcgis.com/en/arcmap/10.3/analyze/python/mapping-fields.htm

[MehdiPira1]

Very useful. Thanks @AndresCastillo 

[AndresCastillo]

Thanks @MehdiPira1 

[NR_McIntyreMurphy__GISS_]

When I use the spatial join tool I am never given the options shown in this blog post. Why am I not seeing the same options?

[FelixHGW]

I have the same problem. I can't find this option at ArcGIS Pro. Is there any other solution at ArcGIS Pro to this? 

Thanks!

[Luke_Pinner]

@FelixHGW click on the source tab, not the properties tab

[FelixHGW]

Ufff. Thanks a lot Luke!

[PawełKropielnicki]

Hey, this method is helping a lot but I have a question about duplicated attributes resaults. 

FID	SHAPE	JOIN COUNT	TARGET FID	CODE
5	Polygon	5	4	20, 20, 20, 41, 20

Is there a way to stop duplicating or to simplify the resault for example instead of having 20, 20, 20, 41, 20 just to accuire only values 20, 41?

Many thanks!

[MarkBryant]

To get rid of duplicated values, you need to run another function on the result. It can't be changed as this is a result of the merge rule.

The code I use is this:

def uniqueValues(the_value, delimiter=","):
    """return unique separated values in order
    Useful to run on ArcGIS processes where there is no control on returned values.
    For example SpatialJoin, JOIN_ONE_TO_ONE, with FieldMapping Merge Rule = Join
    """
    if the_value is None:
        return the_value

    # Create a Python list by splitting the string on the delimeter
    the_list = the_value.split(delimiter)
    # Use set to get unique values
    unique_values = sorted(set(the_list))
    # Reassemble the string from the sorted list
    return delimiter.join(unique_values)