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calculation within an IF statement in arcGIS Pro

MáireDolan

I'll begin by stating I am very new to the python world!

My problem is this....

I am trying to use field calculator in ArcGIS Pro to return a calculation of values in other fields based on an if statement, if that makes sense! Not sure if it can be done?

The Calculation is

Qrp=Sum(Qs*Ls)/SumLs

Basically thus;

weightAADT(!rp!,!Qs!,!Ls!)

Code Block

def weightAADT(rp, Qs, Ls):
if rp=="Urban Two Lane":
return sum(Qs * Ls) / sum(Ls)

my error is "TypeError: 'float' object is not iterable"

Any help appreciated

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FreddieGibson

I would assume that the problem is you're giving the sum built-in function a single number when it expects a collection of numbers.

2. Built-in Functions — Python 3.7.0 documentation

sum(iterable[, start])https://docs.python.org/3/library/functions.html#sum

Sums start and the items of an iterable from left to right and returns the total. start defaults to <SPAN class="">0</SPAN>. The iterable’s items are normally numbers, and the start value is not allowed to be a string.

Are your values Qs and Ls single float values or are they a collection of numbers?

DanPatterson_Retired

The field calculator does one record/row at a time, hence your error as Freddie says.

If you want to vectorize your calculations, you need to use numpy with arcpy's TableToNumPyArray to get the field values into an array format, then arcpy.da.ExtendTable to append the result column onto the original table. Otherwise dump the sum as the error indicates

MáireDolan

Thanks Freddie, that makes sense.

Qs & Ls values are indeed single float values. What I was trying to achieve was to sum the calculation/values for each row containing the value of the if statement.

MáireDolan

Thanks Dan,

I've never used numpy, could you give me an example of its use?

DanPatterson_Retired

If each row contains a Qs and an Ls value, then you can calculate

Qs * Ls as a field calculation …. nothing more.

If the final result is supposed to be the sum of all the (Qs*Ls) values divided by the sum of the Ls values as in

sum(Qs * Ls) / sum(Ls)

then you do that final calculation after the fact by doing a field statistics Sum on that product field and the Ls field.

That equation is a single result which isn't suitable for field calculations

MáireDolan

Thanks Dan,

I have done the above, but was trying to see if I could do the same in one step without the statistics table.

Trying to figure out the most efficient way of doing same.

If the statistics table is it, then I'll go with that.

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