Arcpy Max Value per Group in One Field

Question

I have a point shapefile that have two attributes that I want to extract from them. These two fields are "Group" and "Distance"

I want to grab the maximum "distance" from each unique number in the field "group".

I was wondering if any knew of a method of using arcpy searchcursor to find this max value? Writing something like

rows = arcpy.SearchCursor(input)
  Counter = 0
  for row in rows:
    if row.NEAR_DIST > Counter:
      Counter = row.NEAR_DIST

will only give me the max value of the entire dataset as a whole? Any ideas?

Answer 1

Try this out:

import arcpy

shp = r'C:\Data\Test\test.shp'
rows = arcpy.SearchCursor(shp)

#--first, lets get a list of all unique Group numbers
groups = []
for row in rows:
    if row.Group not in groups:
        groups.append(row.Group)
del row

#--now, lets go back through all rows and find the max for each group
#--and store the results in a dictionary
out_dict = {}
for row in rows:
    for g in groups:
        lst = []
        if row.Group == g:
            lst.append(row.Distance)
        out_dict(g) = max(lst)
del row,rows
for group in out_dict:
    print group

Answer 2

I just don't know about this answer. I tried to get it to work but it won't return the correct max(lst) value. In any case, there is at least one syntax error (should be out_dict[g], not out_dict(g)). It did, however, expose me to dictionaries... and that's a good thing.

I think using the following code would work just fine:

import arcpy

indata = r"C:\indata.shp"
g = ""

for row in arcpy.SearchCursor(indata,"","","", "GROUP A; DISTANCE D"):
if g != row.GROUP:
    g = row.GROUP
    print row.GROUP
    print row.DISTANCE

In any case, this works for me...

Answer 3

with SearchCursor:

import arcpy

workspace = "C:\Data\Test\test.shp"
recs = arcpy.SearchCursor(workspace)

ary = []

for rec in recs:
   val = rec.getValue('Distance')
   ary.append(val)

print max(ary)  

or you can try Summary Statistics (Analysis) tool for your needs. for more information check out here..

Summary

Calculates summary statistics for field(s) in a table.

.

Syntax

Statistics_analysis (in_table, out_table, statistics_fields, {case_field})

Example:

import arcpy
from arcpy import env
env.workspace = "C:/data/Habitat_Analysis.gdb"
arcpy.Statistics_analysis("futrds", "C:/output/output.gdb/stats", [["Shape_Length", 
"MAX"]], "NM")

i hope it helps you...