Field Calculator - Diameter conversion with conditions

[THomasDanks]

Hello,

I am very new with python so have been really struggling with the field calculator for what seems like a simple task. (it is in excel anyway)

I have a shapefile with a column named d_diameter, but this column is String and contains entires; 100mm, 2in,4in, 70in, 50mm, 73mm etc. I am looking to convert these to numbers, specifically to milimeters (mm) and to 2 decimal points.

So ones with "mm" extension, I just want the number. Entries with the "in" extension in I want this removed and the value timesed (*) by 25.4 to convert it to mm.

e.g. 100mm becomes 100 and 2in becomes 50.8 etc

The kicker is sometimes it has NULL values, or Text "Other" or "Unknown". Ideally I want in these cases for it to come through as NULL.

Any idea or input where to start would be greatly appreciated.

Cheers,

Thomas

[JoeBorgione]

Post a sample of how the data is formatted; sounds like the field is of text type and you need the strip off the mm?  Take a look at rstrip — Python Reference (The Right Way) 0.1 documentation ; rstrip is your friend.

Then take a look at the int() function: int — Python Reference (The Right Way) 0.1 documentation  Once you  get rid of the mm, you can treat a string like a number.

Finally, you can use round() to the decimal place of your choice: round — Python Reference (The Right Way) 0.1 documentation 

Untested and probably just one of a myriad of ways to approach it.

[THomasDanks]

Hi,

Thanks for the reply. I tried a similar thing with remove !d_material!.replace("in",("").replace("mm",""). I became stuck though because I only need to multiply the inches e.g. 2in, 4in, 15in by 25.4 and leave the milimeter (mm) ones alone in that caluclation. I didn't know how to do that though. Seems like I need a else if statement, but not sure how to contruct one.

The int function is very good to know thanks. A sample of my data with the column datatype is shown below:

Any ideas?

[DanPatterson_Retired · Accepted solution]

try this but your field calculator expression would be

cal(!YourFieldWithTheOriginalDataHere! 

using the python parser

def cal(a):
    if 'in' in a:
        return str(float(a.split('in')[0])*2.54) + 'mm'
    else:
        return a

a = '9in'
b = '22.86mm'

cal(a)  #'22.86mm'
cal(b)  #'22.86mm'‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

[THomasDanks]

Thanks everyone this worked great. Fantastic!! I'm off to learn some Python!!

[TedKowal]

Pre-Logic Scipt Code:

def dmm (dia):
 if dia is not None:
 units=dia[-2:]
 if units=='in':
 cnv = int(int(filter(str.isdigit,dia))*25.4)
 return str(cnv)+'mm'‍‍‍‍‍‍

YourField=

dmm(str( !d_diameter!))‍‍

[TedKowal]

Dan's is better --- the sample code I was using had unicode strings in it ....

[DanPatterson_Retired]

move to Pro and Python 3. 

Unicode has been covered by python since 3 and I haven't suffered with Unicode issues in over 8 years

[TedKowal]

Love to move to Pro but it does not accept MS Access which is critical to our operations.  The choice of DB's is not mine to make!