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sequential difference in a single column with field calculator

youngpark

Hello,

I have a column for elevation for a point data set. I would like to create a new column to show a difference between Row(n) and Row(n+1) values. well, I assume that the easiest way is calculating in EXCEL (=abs(A1-A2)) then make a join at ArcGIS. However, I would like to the process with "Field calculator" Does anyone know how to do it?

Thanks in advance

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Accepted answers

XanderBakker

To clarify something... you cannot read the next row and store the result in the current row. You can however, remember the previous row and store the difference in the current row. See the example below in ArcGIS Pro (same thing will apply in ArcMap):

You will have to use the Python parser and use the following code in the code block:

prev_val <SPAN class="operator token">=</SPAN> None
<SPAN class="keyword token">def</SPAN> <SPAN class="token function">SequentialDif</SPAN><SPAN class="punctuation token">(</SPAN>curr_val<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">global</SPAN> prev_val
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">if</SPAN> <SPAN class="punctuation token">(</SPAN>prev_val <SPAN class="operator token">==</SPAN> None<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN> 
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; prev_val <SPAN class="operator token">=</SPAN> curr_val 
&nbsp;&nbsp;&nbsp; dif_val <SPAN class="operator token">=</SPAN> curr_val <SPAN class="operator token">-</SPAN> prev_val
&nbsp;&nbsp;&nbsp; prev_val <SPAN class="operator token">=</SPAN> curr_val
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">return</SPAN> dif_val<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

And use this as expression:

SequentialDif(!YourFieldName!)<SPAN class="line-numbers-rows"><SPAN>‍</SPAN></SPAN>

Each record will have the difference between the current and the previous record of the given field.

All comments

youngpark

Thanks Dan,

I should have changed just the field of question. I really appreciate your helps.

DanPatterson_Retired

and if you need the absolute difference, you can get that as well during the calculation process

Python parser of course

Code block below

Expression .... diff_between( !YourFieldName!, absol=True)

<SPAN class="string token">""" -----------------------------------------
diff_between(fld)
input:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; a field
returns:&nbsp;&nbsp;&nbsp; difference between successive records
expression: diff_between(!Shape!)
"""</SPAN>
val <SPAN class="operator token">=</SPAN> <SPAN class="number token">0.0</SPAN>
is_first <SPAN class="operator token">=</SPAN> <SPAN class="token boolean">True</SPAN>
<SPAN class="keyword token">def</SPAN> <SPAN class="token function">diff_between</SPAN><SPAN class="punctuation token">(</SPAN>fld<SPAN class="punctuation token">,</SPAN> absol<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">global</SPAN> val
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">global</SPAN> is_first
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">if</SPAN> is_first<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; is_first <SPAN class="operator token">=</SPAN> <SPAN class="token boolean">False</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; val <SPAN class="operator token">=</SPAN> fld
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">return</SPAN> <SPAN class="number token">0.0</SPAN>
&nbsp;&nbsp;&nbsp; diff <SPAN class="operator token">=</SPAN> fld <SPAN class="operator token">-</SPAN> val
&nbsp;&nbsp;&nbsp; val <SPAN class="operator token">=</SPAN> fld
&nbsp;&nbsp;&nbsp; <SPAN class="comment token">#val = diff</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">if</SPAN> absol<SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">return</SPAN> abs<SPAN class="punctuation token">(</SPAN>diff<SPAN class="punctuation token">)</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">else</SPAN><SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">return</SPAN> diff
<SPAN class="comment token">#__esri_field_calculator_splitter__</SPAN>
<SPAN class="comment token">#diff_between(!YourFieldHere!, True)</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>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

DanPatterson_Retired

Is there any reason you abandoned your duplicate thread?

https://community.esri.com/message/772505-re-field-calculator-to-calculate-diff-row-values-in-a-single-column?commentID=772505#comment-772505

XanderBakker

You will have to use the Python parser and use the following code in the code block:

prev_val <SPAN class="operator token">=</SPAN> None
<SPAN class="keyword token">def</SPAN> <SPAN class="token function">SequentialDif</SPAN><SPAN class="punctuation token">(</SPAN>curr_val<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN>
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">global</SPAN> prev_val
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">if</SPAN> <SPAN class="punctuation token">(</SPAN>prev_val <SPAN class="operator token">==</SPAN> None<SPAN class="punctuation token">)</SPAN><SPAN class="punctuation token">:</SPAN> 
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; prev_val <SPAN class="operator token">=</SPAN> curr_val 
&nbsp;&nbsp;&nbsp; dif_val <SPAN class="operator token">=</SPAN> curr_val <SPAN class="operator token">-</SPAN> prev_val
&nbsp;&nbsp;&nbsp; prev_val <SPAN class="operator token">=</SPAN> curr_val
&nbsp;&nbsp;&nbsp; <SPAN class="keyword token">return</SPAN> dif_val<SPAN class="line-numbers-rows"><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN><SPAN>‍</SPAN></SPAN>

And use this as expression:

SequentialDif(!YourFieldName!)<SPAN class="line-numbers-rows"><SPAN>‍</SPAN></SPAN>

Each record will have the difference between the current and the previous record of the given field.

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