Group attribute tables values for use with conditionals - Python

Question

I would like to group values in a field in an attribute table. The field contains duplicate values. These duplicate values should be grouped based on duplicate values, the field would look something like the arbitrary 'Field' below:

Field   Date    Flagged_Field
X      1/1/2014 
X      1/1/2013 
X      1/1/2015    Y
Y      1/1/2000 
Y      1/1/2008    Y
Z      1/1/1999 
Z      1/1/1998 
Z      1/1/1992 
Z      1/1/2003    Y

Values X, Y and Z which are duplicate records would then be grouped. Ideally I would like to proceed to use if, elif and else to compare other fields within the group containing the value X for Field and once finished move on to the group contain the value Y and lastly Z.

Here's what I have:

cursor = arcpy.SearchCursor(fc)
row = cursor.next()
for row in cursor:
    rowField = (row.getValue("Field"))
    listC = ([list(j) for i, j in groupby(rowField)])
    for groups in listC:
        print str(groups)

What happens is I get a list of unicode for each letter in the field. I believe if I can somehow compare the field values against each other as opposed to the characters in just one field I can get close to what I need with this.

I'm trying to gather all like values based on attributes, specifically one field. I would then like to, using these like values compare other attributes of the data. For example I have a date field which, based on like values in the Field shown in my above example I would like to flag the record containing the most recent date, see revisions above.

Answer 1

I think I understand what you want to do. For each unique value in "Field", you want to find the most recent date in "Date" and set its value to "Y" in "Flagged_Field".
I used your field naming conventions, but you need to avoid using keywords like Field and Date for your field names.

import itertools

def getGrouper(row):
    """Key function to retrieve Field value. Change depending on how you group"""
    return row[0]
def getDate(row):
    """Key function to retrieve Date value. Used in mapping function below"""
    return row[1]
def mostRecentDate(group):
    """Mapping function for retrieving row in each group with most recent date"""
    return max(group, key=getDate)

# I define up here to avoid hard coding into body of script
fc = "YourFeatureClass"
# Column order is important, so define the field names outside cursor definitions
fields = ["Field","Date","Flagged_Field"]
#also putting the index of the flagged field up here, instead of hardcoding
flagindex = 2

# groups is used to store the grouped records for further operations
groups = [] 

# Set search cursor
with arcpy.da.SearchCursor(fc, fields) as cursor:
    # use itertools.groupby to group by Field and then append the results to groups
    for k, g in itertools.groupby(cursor, getGrouper):
        #I do nothing with the key, k, since you only care about the groups, not what they grouped on
        groups.append(list(g))

# At this point you have your groups
# The rest is to do your example of flagging the most recent date

# map groups to the most recent record in each group
flaggedrecords = map(mostRecentDate, groups)
# update records
with arcpy.da.UpdateCursor(fc, fields) as cursor:
    for row in cursor:
        # Very important to tuple the update row, or else you will not have a match
        if tuple(row) in flaggedrecords:
            # If it is in the flagged records, set the flag
            row[flagindex] = 'Y'
        else:
            # Else, unset the flag
            row[flagindex] = ''
        cursor.updateRow(row)