[GIS] Getting first and second row with ArcPy searchcursor

arcpycursor

I have a shapefile with only 4 rows in it. I already could filter it so I have only 2 left. I need these sorted by the 'length' field, then take the first and second row to save in to individual files. Here is the code for sorting:

import arcpy
fc = 'C:\\Users\\test.shp'
fields = ['length', 'FID']
expression = arcpy.AddFieldDelimiters(fc, "length") + " > 1000"
for row in sorted(arcpy.da.SearchCursor(fc, fields,)):
    print('{0}, {1}'.format(row[0], row[1]))

For saving in to the new file:

arcpy.FeatureClassToFeatureClass_conversion(?, outLocation, 
                                            outFeatureClass,)

How can I make the search cursor to show first only the lower value row, then the higher one? (order doesn't matter)

How can I select the number 1 row, then the number 2 row?

Best Answer

You do not state what your license level is; this is always important as it dictates the solution. Having said that, consider using the Sort tool (which requires an Advanced license). More information can be found here.

Related Solutions

[GIS] Using Update Cursor in a double for loop in arcpy

You don't need a nested loop (and it's written in a wrong way because you will scan your table only once)

So. First of all read all the data from the table and sum it up.

data = {}
with arcpy.da.SearchCursor(table_datei, ["src_FID", "LENGTH"]) as sc:
    for row in sc:
        try:
            data[row[0]] = data[row[0]] + row[1]
        except KeyError:
            data[row[0]] = row[1]

This will give you a dictionary {data} with keys as your FID and values as a sum of all lenghts linked to this FID.

Next, start an update cursor and write it to your FC:

with arcpy.da.UpdateCursor(param_polygone, ["FID", "Nbr_Laenge"]) as uc:
    for row in uc:
        row[1] = data[row[0]]
        uc.updateRow(row)

That's it.

ArcPy – Comparing Values with Next Row Using Cursor

Like @PolyGeo said, list comprehensions will help. I notice, too, that you don't define counter in your code block. Without understanding what it is, I've included it as I think you meant to have it.

    field1_list = [row[0] for row in arcpy.da.SearchCursor(tab_selektiert, ["field1"])]
    field2_list = [row[0] for row in arcpy.da.SearchCursor(tab_selektiert, ["field2"])]

    #Assuming here that counter must initialize at 1. If if should initialize at 0,
    # just change it.
    counter = 1 
    index = 0

    with arcpy.da.UpdateCursor(tab_selektiert, ["markerfield"]) as updater:
        for row in updater:
            #The value of index should never exceed len-2, since len is always
            # 1 more than the highest index value, and your function will only
            # check up to the next-to-last item in the list (the last item has
            # nothing to compare to
            if index<=len(field1_list)-2:
                n0 = field1_list[index] #The field1 value for current index
                n1 = field2_list[index] #The field2 value for the current index
                n2 = field1_list[index+1] #The field1 value for the next index
                n3 = field2_list[index+1] #The field2 value for the next index

                if n1==n2 or n3==n0 or n0==n2:
                    #EDIT: Index only increases if none of the numbers
                    # match. The markerfield is always updated with
                    # counter. 
                else:
                    #This is the condition where counter is increased
                    counter+=1

                updater.updaterRow([counter])
                index+=1

            else:
                #If you've reached the last item, update the last row with counter,
                # then break out of the loop
                updater.updateRow([counter])
                break

It's worth noting that you said counter= +1, but in python the way to do what you're trying to do is as I have it: counter+=1. I hope this helps!

Best Answer

Related Solutions

[GIS] Using Update Cursor in a double for loop in arcpy

ArcPy – Comparing Values with Next Row Using Cursor

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