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Im creating a script to calculate some new fields in Arcgis10.1 using the arcpy library. I need to sum the total of a table column in order to calculate a new field. I wanted to ask if it is possible to store all the values in an array so i can get the total sum and use the variable in the new field calculation?

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summed_total = 0
with arcpy.da.SearchCursor(fc, "field to be totaled") as cursor:
    for row in cursor:
        summed_total = summed_total + row[0]

Something like this would work. Replace what's in quotes with your field name, or with a list of fields you're going to be working with. Replace fc with the feature that holds the field.

That won't work for 10.0 or earlier; da.SearchCursor didn't show up until 10.1. For earlier versions:

summed_total = 0
field = "field to be summed"
with arcpy.SearchCursor(fc):
    for row in cursor:
        summed_total = summed_total + row.GetValue(field)
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    the data access module (resources.arcgis.com/en/help/main/10.1/index.html#//…) was introduced at 10.1 – Nxaunxau Jan 8 '14 at 2:26
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    Yep, you're right. Ignore that second example, the da.SearchCursor is a much better option. – HeyOverThere Jan 8 '14 at 2:26
  • This worked pretty good i made some small changes to fit my script but overall it was exactly what needed – Daniel Jimenez Jan 8 '14 at 17:22
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    Here's the one-liner: summed_total = sum((r[0] for r in arcpy.da.SearchCursor(fc, ['FIELDNAME']))) – nmpeterson Oct 7 '14 at 14:12
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You can accomplish this in two lines when working with numpy arrays (TableToNumPyArray).

import arcpy, numpy

fc = r'C:\path\to\your\fc'

# Convert to numpy array.  "test" is the field name
field = arcpy.da.TableToNumPyArray (fc, "test", skip_nulls=True)
sum = field["test"].sum() 

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