How can I calculate a "moving" conditional evaluation in Field Calculator?

Stefande_Bruin1

Hi

I was wondering if anyone has ever tried doing this kind of calculation in field calculator, or if it is even possible. What I am trying to do is to calculate an order field, based on repeating polyline IDs. In excel I would do something like "If ID2 = ID1, Order1 + 1, else 1. In essence, the query refers to another column and to itself, and it refers to specific rows, sometimes other than the row being calculated. Is this doable with a VB or Python script?

Best regards

Stefan

JoshuaBixby

The following should work in Pro, not sure about ArcMap since it uses Python 2.x.

Code Block:

<SPAN class="keyword token">from</SPAN> collections <SPAN class="keyword token">import</SPAN> defaultdict

<SPAN class="keyword token">def</SPAN> <SPAN class="token function">counter_gen</SPAN><SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN>
    counter <SPAN class="operator token">=</SPAN> defaultdict<SPAN class="punctuation token">(</SPAN>int<SPAN class="punctuation token">)</SPAN>
    v <SPAN class="operator token">=</SPAN> None
    <SPAN class="keyword token">while</SPAN> <SPAN class="token boolean">True</SPAN><SPAN class="punctuation token">:</SPAN>
        counter<SPAN class="punctuation token">[</SPAN>v<SPAN class="punctuation token">]</SPAN> <SPAN class="operator token">+=</SPAN> <SPAN class="number token">1</SPAN>
        v <SPAN class="operator token">=</SPAN> <SPAN class="keyword token">yield</SPAN> counter<SPAN class="punctuation token">[</SPAN>v<SPAN class="punctuation token">]</SPAN> <SPAN class="keyword token">if</SPAN> v <SPAN class="keyword token">else</SPAN> None
        
g <SPAN class="operator token">=</SPAN> counter_gen<SPAN class="punctuation token">(</SPAN><SPAN class="punctuation token">)</SPAN>
next<SPAN class="punctuation token">(</SPAN>g<SPAN class="punctuation token">)</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

and Expression:

g<SPAN class="punctuation token">.</SPAN>send<SPAN class="punctuation token">(</SPAN>!ID!<SPAN class="punctuation token">)</SPAN><SPAN class="line-numbers-rows"><SPAN>‍</SPAN></SPAN>

The code above works whether the table is sorted by ID groups or not.  If the table is sorted by some other column, the code just takes the first ID value x and makes it 1, the second ID value x as 2, etc.... as it finds them.