Optimizing UpdateCursor Script

Question

Hello everyone,

I'm building a script to calculate offset values for linearly referenced data based on how many times distance values occur in a dataset. This is the script I've come up with and it works how I'd like it to, though once applied to the 6,000+ piece dataset it takes hours to complete.

Any thoughts on how I might be able to speed it up?

#pt table
pt_tbl = 'ArcPRO_MasterQuery_EXT_pt'

with arcpy.da.SearchCursor(pt_tbl, "NUM_SEC") as cursor2:
    traillist = []
    tns = set(cursor2)
    for thing in tns:
        for d in thing:
            traillist.append(d)
    traillistsortpt = sorted(traillist)

print("Calculating Point Table Offsets...")

traillistsortpt = ["11-1", "11-2"]

i = 0
for num in traillistsortpt:
    arcpy.management.SelectLayerByAttribute(pt_tbl, "NEW_SELECTION", "NUM_SEC = '%s'" %(num))

oor = {}
    oo  = {}

with arcpy.da.UpdateCursor(pt_tbl, ["OID@", "DISTANCE", "DESCRIPTION_1", "DESCRIPTION_2", "DESCRIPTION_3", "Offset"]) as cursor1:
        for row in cursor1:
            distance_value = row[1]
            oo[distance_value] = oo.get(distance_value, 0) +1

if "RHS" in str(row[2]) or "RHS" in str(row[3]) or "RHS" in str(row[4]):
                oor[distance_value] = oor.get(distance_value, 0) + 1

orh = (oo[distance_value] - 1) * -1
                row[5] = orh

elif row[1] in oor:
                o = (oo[distance_value] - (oor[distance_value]+1))
                row[5] = o
            else:
                o = (oo[distance_value] - 1)
                row[5] = o

cursor1.updateRow(row)

i+=1
    print(i, " of ", len(traillistsortpt))

arcpy.management.SelectLayerByAttribute(pt_tbl, "CLEAR_SELECTION")
print("Point Table Offsets Calculated")

MErikReedAugusta · Answer

I feel like this post solves all of the main issues I saw really well, but I want to emphasize a couple points that burned me early on, when I couldn't figure out why my code was taking forever to run:

1. The Data Access Cursors have a ton of work to do and can be more computationally intensive than you might think.  Avoid calling them inside loops like this unless you want to go through your whole dataset multiple times.  (Especially avoid calling Cursor loops inside other Cursor loops.  That way madness lies.)  It's often much better for the Cursor to be your outermost loop, and do whatever other operations you have to do inside that cursor loop.

2. @JoshuaBixby 's comment up above condensing your first Cursor is a great example of using the speed of list comprehension to your advantage.  To avoid getting technical, even though his script looks like it's just a compression of yours into a single line, it's more efficient than even just that.  List comprehension does a bunch of stuff behind the scenes in more efficient form, and you can often save processing time there.

blake.terhune · Answer

I'm not going to touch the logic you have that calculates offset. You'll need to review that on your own.

pt_tbl = "ArcPRO_MasterQuery_EXT_pt"

pt_tbl_fields = ["DISTANCE", "DESCRIPTION_1", "DESCRIPTION_2", "DESCRIPTION_3", "Offset"]
trail_num_sec = ["11-1", "11-2"]
comma_sep_str = ",".join([f"'{i}'" for i in trail_num_sec])
expression = f"NUM_SEC in({comma_sep_str})"

oor = {}
oo  = {}
with arcpy.da.UpdateCursor(pt_tbl, pt_tbl_fields, expression) as u_cursor:
    for distance, desc_1, desc_2, desc_3, offset in u_cursor:
        oo[distance] = oo.get(distance, 0) + 1

if "RHS" in [desc_1, desc_2, desc_3]:
            oor[distance] = oor.get(distance, 0) + 1

offset = (oo[distance] - 1) * -1

elif distance in oor:
            offset = (oo[distance] - (oor[distance]+1))
        else:
            offset (oo[distance] - 1)

u_cursor.updateRow([distance, desc_1, desc_2, desc_3, offset])

print("Point Table Offsets Calculated")

blake.terhune · Answer

* As @DavidPike mentioned, your variable naming makes your code unnecessarily hard to follow.
* The SearchCursor portion that builds the traillistsortpt list is immediately overwritten with hardcoded values on line 14. Why?
* You can use enumerate() to count iterations of a thing instead of counting it yourself with i
* At the very least, use the string format() method instead of the old %s operator. If you're working in ArcGIS Pro (Python 3), use the f-string
* Declaring cursors outside the loop is more performant because it won't get recreated with every iteration of the loop.
* Sequence unpacking can sometimes be a convenient way to name the cursor's individual values instead of referring to them by their row index. It gets a bit much if you have more than a handful of fields though, in which case you could make each row a dictionary with field names.
* You should utilize the where_clause parameter of the UpdateCursor instead of making a selection.
* Your logic for setting the Offset field value (row[5]) seems flawed. You're checking for a value in oor before you put the value in oor.