How do I count occurrences of unique field values?

Question

I have a feature class with a field which contains values 1, 2 and 3. I need to write code that reports the total count for each value:

1: 29 features

2: 52 features

3: 57 features

This is my code so far:

print "start"
import arcpy
arcpy.env.overwriteOutput = 1

fc = r"D:\AVI_DAVID\zevel\zevel.gdb\Export_Output_miv_cur"
lst_field = arcpy.ListFields(fc,"USAGE") #usage is the field
for f in lst_field:
    print f.name

Do I need a SearchCursor? Or an UpdateCursor?

Answer 1

@nmpeterson's answer is a good one. If you don't want to create a table you can get this information as a SearchCursor. You can do it by making use of a dictionary to tally counts:

import arcpy

fc = r"D:\AVI_DAVID\zevel\zevel.gdb\Export_Output_miv_cur"
field = "USAGE"

#Create dictionary to store unique values
CountDi = {}

with arcpy.da.SearchCursor (fc, field) as cursor:
    for row in cursor:
        if not row[0] in CountDi.keys():
            CountDi[row[0]] = 1
        else:
            CountDi[row[0]] += 1

for key in CountDi.keys():
    print str(key) + ":", CountDi[key], "features"

An alternative would be using lists and sets:

import arcpy

fc = r"D:\AVI_DAVID\zevel\zevel.gdb\Export_Output_miv_cur"
field = "USAGE"

Occurances = []
with arcpy.da.SearchCursor (fc, field) as cursor:
    for row in cursor:
        Occurances.append (row[0])

for i in set(Occurances):
    icount = Occurances.count(i)
    print str(i) + ":", icount, "features"

Many ways to skin a python. Note that this makes use of the data analysis search cursor, which requires ArcGIS 10.1 or newer.

Answer 2

There is a tool in ArcGIS called "Frequency" (arcpy.Frequency_analysis()) that allows to to count the number of occurrences of each unique value in a specific field (or unique combinations of values in multiple fields). It will create a new table containing the original field name(s) with a row for each unique value/combination, and another "Frequency" field containing the number of rows in the original feature class with that particular value.

In your case, the arcpy call would look like this:

arcpy.Frequency_analysis(fc, PATH_TO_OUTPUT_TABLE, ["USAGE"])

Answer 3

Summary Statistics with a case_field will produce a table with <value>, FREQUENCY

Stand Alone:

<output_object> = arcpy.Statistics_analysis(<in_layer>,
                                      "in_memory\\<out_table_name>",
                                      [['<field_to_count>', 'COUNT']], '<field_to_count>')

Python Window:

    arcpy.analysis.Statistics("<layer_name>", r"<path_and_output_shp>", "<field_to_count> COUNT", "<field_to_count>")