topic Re: How to determine number of records using arcpy.da.SearchCursor in Python Questions

How to determine number of records using arcpy.da.SearchCursor

BruceBacia — Fri, 21 Mar 2014 17:46:52 GMT

Does anyone know of a quick way to return the number of records in a query constrained Search Cursor using the da module?

rows = arcpy.da.SearchCursor(someFC,someFields,someQuery)  print (len(rows))  #I'm sure this used to work with the old cursors, but doesn't work with da.SearchCursor

Re: How to determine number of records using arcpy.da.SearchCursor

JamesCrandall — Sat, 11 Dec 2021 15:02:25 GMT

This works (and should honor any selections):


myFeatClass = r'C:\MyGDB\myFeatureClass'
result = int(arcpy.GetCount_management(fc).getOutput(0))

print result

This also works:


rowcount = 0
myFeatClass = r'C:\MyGDB\myFeatureClass'
with arcpy.da.SearchCursor(myFeatClass, "*") as cursor:
    for row in cursor:
        count = count + 1

print rowcount

Edit: You can also apply an sql conditional statement too


rowcount = 0
sql = "OBJECTID = 29821"
myFeatClass = r'C:\MyGDB\myFeatureClass'
with arcpy.da.SearchCursor(myFeatClass, "*", sql) as cursor:
    for row in cursor:
        count = count + 1

print rowcount

Re: How to determine number of records using arcpy.da.SearchCursor

BruceBacia — Fri, 21 Mar 2014 19:20:24 GMT

Thanks for the suggestions, but I'm looking to avoid a counter.

Re: How to determine number of records using arcpy.da.SearchCursor

JamesCrandall — Fri, 21 Mar 2014 19:22:51 GMT

Thanks for the suggestions, but I'm looking to avoid a counter.

arcpy.GetCount_management doesn't work for you?

Re: How to determine number of records using arcpy.da.SearchCursor

MattEiben — Fri, 21 Mar 2014 21:34:08 GMT

You were actually very close in your original entry. Try this:

rows = [row for row in arcpy.da.SearchCursor(someFC,someFields,someQuery)]  print len(rows)

The cursor creates an iterator, which you can't find the length of. The key is to use list comprehension for a nice one liner with the cursor to make your list.

Of course, you can always just this as an alternative:

int(arcpy.GetCount_management(someFC).getOutput(0))

Hope this helps!

Re: How to determine number of records using arcpy.da.SearchCursor

JasonScheirer — Sat, 11 Dec 2021 15:02:28 GMT

Please, please, please use James' GetCount solution:

result = int(arcpy.GetCount_management(fc).getOutput(0))

It will be the fastest.

Re: How to determine number of records using arcpy.da.SearchCursor

FilipKrál — Sat, 11 Dec 2021 15:02:30 GMT

Indeed, use arcpy.GetCount_management. In order to limit the number of record by a where clause, create a feature layer (or table view) first.

fc = r'c:\path\to\fc'
w = '"OBJECTID" < 10'
lr = arcpy.MakeFeatureLayer_management(fc, 'tmp_layer', w).getOutput(0)
result = int(arcpy.GetCount_management(lr).getOutput(0))
arcpy.Delete_management(lr) # deletes the layer, not the feature class data
# result is 9

Re: How to determine number of records using arcpy.da.SearchCursor

benberman — Tue, 25 Mar 2014 02:08:03 GMT

I actually just built one like this today.

lst = [row.getvalue() for row in arcpy.SearchCursor(dataset,expression...enter other parameters you want to include)]
print len(lst)

Re: How to determine number of records using arcpy.da.SearchCursor

benberman — Tue, 25 Mar 2014 02:12:59 GMT

I would err on the side of the SearchCursor rather than GetCount in case if a request may arise when he may need to include queries on the dataset.

Re: How to determine number of records using arcpy.da.SearchCursor

ChrisSnyder — Sat, 11 Dec 2021 15:02:33 GMT

The number of records determines what method (GetCount or da.SearchCursor) is faster.

If the number of records is quite large, GetCount is faster, otherwise the searchcursor one liner is faster. I use the latter method (cursor) in some code that recursively (and quickly) needs to determine selected set counts.

Jason - Curious why you indicate the cursor method is a poor choice (locks?, memory?, ???).

import arcpy, time
fc = r"C:\csny490\overlay_20130620\ldo_20130620\ldo_database.gdb\crew_code"
time1 = time.clock()
result = int(arcpy.GetCount_management(fc).getOutput(0))
time2 = time.clock()
print "GetCount (" + str(result) + "), took " + str(time2-time1) + " seconds..."
time1 = time.clock()
result = len([r[0] for r in arcpy.da.SearchCursor(fc, ["OID@"])])
time2 = time.clock()
print "SearchCursor (" + str(result) + "), took " + str(time2-time1) + " seconds..."

Some results:

Table with 8 records:
GetCount (8), took 0.755854384327 seconds...
SearchCursor (8), took 0.136624540949 seconds...

Table with 81k records:
GetCount (81327), took 0.996590826688 seconds...
SearchCursor (81327), took 0.648470391747 seconds...

Table with 2 mm records:
GetCount (2133404), took 4.37459715564 seconds...
SearchCursor (2133404), took 11.5886194669 seconds...

Re: How to determine number of records using arcpy.da.SearchCursor

JasonScheirer — Tue, 25 Mar 2014 19:18:14 GMT

@Chris -- because of that last, millions-of-records result. There's a certain amount of time required to set up/tear down a GP tool (which is what's causing the first two results in your benchmarks to look the way they do), but a for loop in a core GP tool looping over rows in its native ArcObjects/C++ implementation will be orders of magnitude faster than that of a for loop in Python, not to mention GetCount can do other tricks that the Python code isn't doing like seeing if there is a selection set on the table or layer, and if so just asking for the length of the list of selected records without needing to open a cursor on the actual data.

Re: How to determine number of records using arcpy.da.SearchCursor

ChrisSnyder — Sat, 11 Dec 2021 15:02:36 GMT

Jason - thanks for the explanation. For the smaller record counts, I too noticed the slight overhead (set up/tear down a GP tool) of the GetCount tool, which is why I started using the cursor method (which didn't seem to have the extra overhead that GetCount does). In my case, I had some code that needed to inspect a recursive feature count hundreds/thousands of times in a loop, and I found the cursor method (because the record count was relatively small) was the best performer (BTW: using the .fidSet describe property was the worse).

Per the count of the selected set, you can of course do it like:

arcpy.MakeFeatureLayer_management(fc, "fl1")
arcpy.SelectLayerByAttribute_management("fl1", "NEW_SELECTION", "LAND_COVER_CD in (41,42)")
result = len([r[0] for r in arcpy.da.SearchCursor("fl1", ["OID@"])])
#Or this if you don't need an actual "selected set"...
result = len([r[0] for r in arcpy.da.SearchCursor(fc, ["OID@"], "LAND_COVER_CD in (41,42)")])

Re: How to determine number of records using arcpy.da.SearchCursor

BruceBacia — Thu, 03 Apr 2014 11:55:15 GMT

Thanks for all of the helpful posts. This script works with Workflow Manager, and I think that with my current workflow(below), if I used GetCount, I would have to make 2 feature layers. So I'll go with len([r for r in arcpy.da.SearchCursor....])

Workflow
-Use .sde connection file to connect to default version of database.
-Get what should be a unique polygon attribute (but isn't always unique) from WMX for a SQL query.
-Make feature layer of whole feature class without SQL query (The whole feature class is created because the polygon may or may not yet exist in default - rec and posts are scheduled nightly)
-Change version (based on WMX user)
-Create SearchCursor on version, using SQL query to limit records, and get len(SearchCursor) (Here I could create another feature layer using the SQL query, in order to be able to use GetCount. Seems inefficient?)
-Based on number of records in search cursor(>1, 1, or 0), do stuff.

Re: How to determine number of records using arcpy.da.SearchCursor

Leandro-Zamudio — Sat, 11 Dec 2021 15:02:38 GMT

I'd suggest you to encapsulate it into a function. I developed a tiny function called SearchCounter derivated from a Validator in a previous blog post.

def SearchCounter(cursor):
     counts = 0
     for counter in cursor:
          counts += 1;
     cursor.reset()
     return counts

#Previous Code
#...
RecordCount = SearchCounter(arcpy.da.SearchCursor(Table,Fields,Query))
#...
#End Code

Greetings

Re: How to determine number of records using arcpy.da.SearchCursor

nlibassi-col — Thu, 30 Jan 2025 16:25:06 GMT

This also now works:

with arcpy.da.SearchCursor(table, fields, query) as cursor: rows = list(cursor) row_count = len(rows)

...though you would then need to re-create the cursor if you want to iterate over the rows for something else.