topic Re: Count features in geodatabase in Python Questions

Count features in geodatabase

MihaKlemencic — Fri, 10 Dec 2021 21:04:48 GMT

I am new to python and I would to like to count the number of features in each feature class that meet certain criteria.

In geodatabase I have many feature classes. One of the attribute field has values "number/number" --> 50/2, 99/6

I would to like to loop each feature class, select layer by attribute and count selected features, which contain sign "/" and print the result. Below is python code:

import arcpy

#Set the input workspace
arcpy.env.workspace = "d:/TMP/miha_k/zirovnica/novo/test.gdb"

fcs = arcpy.ListFeatureClasses()
cursor = arcpy.SearchCursor(fcs)

for row in fcs:
      arcpy.SelectLayerByAttribute_management(fcs, "NEW_SELECTION", "PARCELA LIKE '%/%'")
      arcpy.GetCount_management(fcs)
      print row‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

I would appreciate your help

Re: Count features in geodatabase

DanPatterson_Retired — Wed, 22 Feb 2017 17:14:44 GMT

taking a wild guess that you got an error... what was it? what field are you querying in each table? is there any similarity between the tables? Have you done this manually? can you put your workflow into a model?

Just some ideas to get you started

Re: Count features in geodatabase

DarrenWiens2 — Wed, 22 Feb 2017 17:35:48 GMT

A few things:

- Cursors cycle through individual features within a feature class/table. You don't seem to need that here.

- When you do 'for row in fcs:', the individual feature class is called row. The list of feature classes is fcs. So, you should select from row, not fcs.

- Refer to the help for GetCount, especially the example. Note that it returns a result, not a number.

Re: Count features in geodatabase

RandyBurton — Fri, 10 Dec 2021 21:04:51 GMT

As Darren suggested, I don't think you would want to cycle through all your features; they might not have the fields you want to query anyway.

Here's some code based on this link:

arcpy.env.workspace = r"d:/TMP/miha_k/zirovnica/novo/test.gdb"
in_table = "featureToSearch"

# MakeTableView_management (in_table, out_view, {where_clause}, {workspace}, {field_info})
arcpy.MakeTableView_management(in_table, "myTableView", "PARCELA LIKE '%/%'")
count = int(arcpy.GetCount_management("myTableView").getOutput(0))‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

But, if your features all contain the same field in your where query, you could do a "for row in fcs" loop. You could also add an if "feature in list" line to limit the features used.

Re: Count features in geodatabase

MihaKlemencic — Wed, 22 Feb 2017 18:23:16 GMT

Field "PARCELA" exits in all tables.

The workflow is:

select by attributes
write query "PARCELA LIKE '%/%'"
Count selected features

But doing this workflow manually on more than 100 feature classes is time consuming.

Re: Count features in geodatabase

RandyBurton — Fri, 10 Dec 2021 21:04:54 GMT

To loop through all the features, you might try the following code. However, if the where clause fails, you may get a count of all records.

import arcpy

arcpy.env.workspace = r"d:/TMP/miha_k/zirovnica/novo/test.gdb"

fcs = arcpy.ListFeatureClasses()

for row in fcs:
    arcpy.MakeTableView_management(row, "myTableView", "PARCELA LIKE '%/%'")
    print row, int(arcpy.GetCount_management("myTableView").getOutput(0))
    arcpy.Delete_management("myTableView")
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Count features in geodatabase

DarrenWiens2 — Fri, 10 Dec 2021 21:04:56 GMT

Just to add that you can test whether or not there is a selection by inspecting the describe FIDSet property:

... if arcpy.Describe(fc).FIDSet == '':
...     print 'There is no selection'
... else:
...     print 'There is a selection'‍‍‍‍

Re: Count features in geodatabase

JoshuaBixby — Wed, 22 Feb 2017 19:26:36 GMT

FIDSet is a Layer property, calling it will generate an attribute error if Describe is passed a feature class directly. If a table view or feature layer is passed to Describe, then FIDSet should return a value, but I think rvburton‌ approach obviates the need for checking FIDSet.

Re: Count features in geodatabase

DarrenWiens2 — Wed, 22 Feb 2017 19:38:32 GMT

Ah, yes, that's right. I was back on the original idea of using SelectLayerByAttributes, which now that I look at it, needs to be preceded by MakeFeatureLayer (or MakeTableView).

Re: Count features in geodatabase

MihaKlemencic — Wed, 22 Feb 2017 20:47:45 GMT

Thanks for help

Really need to learn python for ArcGIS. Can you suggest any of books?

Re: Count features in geodatabase

RebeccaStrauch__GISP — Wed, 22 Feb 2017 20:55:31 GMT

There are quite a few threads in the forum for learning Python. Do a quick search and you can find them. Here is a start

Re: Count features in geodatabase

RandyBurton — Wed, 22 Feb 2017 22:03:01 GMT

1. Follow Dan Patterson‌'s Py... blog.

2. Check out Some Python Snippets

3. Free online courses like Tutorials Point

Re: Count features in geodatabase

MihaKlemencic — Thu, 23 Feb 2017 18:57:19 GMT

What can you say about book Programming ArcGIS with Python Cookbook (second edition) By Eric Pimpler?

Re: Count features in geodatabase

RandyBurton — Thu, 23 Feb 2017 19:46:24 GMT

The Programming ArcGIS with Python Cookbook book looks like a good resource and worth the investment. I have found online resources to be just as valuable, if not more so, than a few good reference books. Knowing what and how to ask Google (etc.) is an invaluable skill.

Re: Count features in geodatabase

RebeccaStrauch__GISP — Thu, 23 Feb 2017 19:49:47 GMT

I was just looking for an answer to something, and came up with this online version (and found my answer)

Dive Into Python

Re: Count features in geodatabase

DanPatterson_Retired — Thu, 23 Feb 2017 20:07:21 GMT

python on GitHub and python.org once the introductions are done, these are the source links to which all refer. A slog perhaps? Not really if you like clarity and brevity

Re: Count features in geodatabase

MaxMarno — Fri, 10 Dec 2021 21:04:59 GMT

Try the following function (first substituting the field index number for '10' for your search field.

def countfeaturesfun(inFC):
    with arcpy.da.SearchCursor(inFC, "*") as cursor:
        Count = 0
        for row in cursor:
            if "/" in str(row[10]):
                Count+=1
    return Count‍‍‍‍‍‍‍

Re: Count features in geodatabase

DarrenWiens2 — Fri, 10 Dec 2021 21:05:02 GMT

Technically, this works. I'm not always the one to do things the "right" way either, but there are a few reasons not to do it this way:

- you need to manually count the field index

- this method reads every feature in the feature class. Using a where clause only reads the matching features, through the magic of SQL, which I don't understand, but from the help, "When a query is specified for an update or search cursor, only the records satisfying that query are returned." Anyhow, it seems to take about 3x longer to read through everything, but it likely depends on the data and how many matches there are. Also, to be fair, the results below are representative of several runs, except the first run, which adds about 3s in actually constructing the table view. So, I suppose the main point is that this method is just fine for small data sets, but likely worse for large data sets.

import timeit
fc = 'bc_geoname_albers' # ~45,000 features

# SQL method
start_time = timeit.default_timer()
arcpy.MakeTableView_management(fc, "myTableView", "CGNDBKEY LIKE '%C%'")
Count = int(arcpy.GetCount_management("myTableView").getOutput(0))
print (Count,str(timeit.default_timer() - start_time))

# Count method
start_time = timeit.default_timer()
with arcpy.da.SearchCursor(fc, "*") as cursor:
    Count = 0
    for row in cursor:
        if "C" in str(row[4]):
            Count+=1
print (Count,timeit.default_timer() - start_time)

(13531, 0.64809157931) # SQL method: 0.65s
(13531, 1.87391371297) # Count method: 1.87s‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Count features in geodatabase

MaxMarno — Fri, 24 Feb 2017 00:03:32 GMT

Agreed, in considering processing time, your version would be quicker and more reliable. However like you noted as well for a smaller dataset the difference would be negligible. Cheers to SQL!