topic Re: Remove first 2 characters using if statement in Python Questions

Remove first 2 characters using if statement

AmyKlug — Fri, 09 Aug 2013 21:54:29 GMT

Hi, I would like to have this code remove and XY or RR (if they are the first 2 characters) in a field with values

XY2365541
RR1247884
8965445

would be:

2365541
1247884
8965445

Writing a query is giving me trouble. I was trying this code with a search cursor, getvalue and if elif statement...but no luck

import arcpy Feature_Class_Name = arcpy.GetParameterAsText(0) Output_Features = arcpy.GetParameterAsText(1) arcpy.env.workspace = r"H:/TestMDB.gdb/XY_1"  cursor = arcpy.da.UpdateCursor(Feature_Class_Name, ["NM"]) for row in cursor:     cursor.updateRow([row[0][2:]]) del fc

Re: Remove first 2 characters using if statement

DanPatterson_Retired — Fri, 09 Aug 2013 22:10:49 GMT

is pseudo code
avalue (a row value in string format)
prefix = ["XY", "RR"]
if avalue[0:2] in prefix:
avalue = avalue[2:]
print avalue

Re: Remove first 2 characters using if statement

AmyKlug — Mon, 12 Aug 2013 17:00:46 GMT

is pseudo code
avalue (a row value in string format)
prefix = ["XY", "RR"]
if avalue[0:2] in prefix:
avalue = avalue[2:]
print avalue

not really sure what to do here

Re: Remove first 2 characters using if statement

T__WayneWhitley — Mon, 12 Aug 2013 17:08:53 GMT

Dan said you "here's your pseudocode", so you have to test something out -- this line is wrong:

cursor.updateRow([row[0][2:]])

...believe you have to set the row field val 1st then update the row...as in something like:

row[0] = row[0][2:]
cursor.updateRow(row)

Try that substitution...actually, I think you specified you wanted to test for the 1st 2 char, then substitute something else - so you'll need an 'if' statement, plenty of examples in the web help. Make a copy of your fc, and start experimenting, following the above for starters.

Enjoy,
Wayne

Re: Remove first 2 characters using if statement

AmyKlug — Mon, 12 Aug 2013 19:27:29 GMT

Dan said you "here's your pseudocode", so you have to test something out -- this line is wrong:

cursor.updateRow([row[0][2:]])

...believe you have to set the row field val 1st then update the row...as in something like:

row[0] = row[0][2:]
cursor.updateRow(row)

Try that substitution...actually, I think you specified you wanted to test for the 1st 2 char, then substitute something else - so you'll need an 'if' statement, plenty of examples in the web help. Make a copy of your fc, and start experimenting, following the above for starters.

Enjoy,
Wayne

I will be more specific......

is pseudo code
avalue (a row value in string format)
prefix = ["XY", "RR"]
if avalue[0:2] in prefix:
avalue = avalue[2:]
print avalue

I read this as.......if row[0:2] in ["XY", "RR].........this makes no sense to me. Row[0:2] is a row value such as XY885442554 and nothing I have tried recognizes ["XY, "RR"]. Do I need to also use a search cursor?

Re: Remove first 2 characters using if statement

DanPatterson_Retired — Mon, 12 Aug 2013 19:42:19 GMT

Within a cursor of some form (insert possibly in your case), if the first two characters ( [0:2] ) are "XY" or "RR" are found within the offending list ["XY", "RR"], substitute/update your field/row with the value with those values removed.

It is hard to debug someone else's code unless you have field calculator syntax that works before you move on to automating the process to include multiple cases. Try to simply the operation by performing single steps at a time (eg. strip off "XY" if it is contained within a field) then move onto the next selection finding fields that begin with "RR" and stripping those off. If this is a one-off deal you are done...if this is daily, then generate a field calculator expression which covers all cases. I often find the former faster than the latter and I have been coding for years.

Re: Remove first 2 characters using if statement

T__WayneWhitley — Sun, 12 Dec 2021 06:42:09 GMT

Yes, maybe the 'stumbling block' here is the isolation of text to trim, or at least selecting those for some kind of conditional 'slicing' or text formatting, whatever -- so I have found the best way to grow more accustomed to how Python handles string handling is to test something interactively, say in IDLE or ArcMap's python window. You can even test expressions in the field calculator - as long as you have saved a copy of your data, you can practice, no matter really if it succeeds/fails or even crashes/freezes ArcMap, think we've all done that...restart and try again.

Having said that, check out this behavior using IDLE:

>>> bunchOfValues = ('XY885442554', 'TY3485694873', 'RR473892711')
>>> print bunchOfValues
('XY885442554', 'TY3485694873', 'RR473892711')
>>> 
>>> for eachValue in bunchOfValues:
 print eachValue

 
XY885442554
TY3485694873
RR473892711
>>> 
>>> for eachValue in bunchOfValues:
 if eachValue[0:2] in ['XY', 'RR']:
  print eachValue[2:]
 else:
  print eachValue

  
885442554
TY3485694873
473892711
>>>

...still want more, see this, the skinny:
http://stackoverflow.com/questions/509211/the-python-slice-notation

Re: Remove first 2 characters using if statement

AmyKlug — Sun, 12 Dec 2021 06:42:12 GMT

Thanks Dan and Wayne.....that really helped. Here is the final code:

>>> import arcpy
>>> fc = r"H:/Test.gdb/NameTest"
>>> cursor = arcpy.da.UpdateCursor(fc, ["NM"])
>>> for row in cursor:
...     row = row[0]
...     if row[:2] == "XY":       
...         cursor.updateRow([row[2:]])       
...     elif row[:2] == "RR":    
...         cursor.updateRow([row[2:]])
...     else:    
...         print "Name field is alread up-to-date"
>>>> del fc, cursor

Re: Remove first 2 characters using if statement

DanPatterson_Retired — Sun, 12 Dec 2021 06:42:14 GMT

To emphasize the useage of the "in" list operand consider the following:

>>> bunchOfValues = ['XY885442554', 'TY3485694873', 'RR473892711']
>>> for aValue in bunchOfValues:
...  if aValue[:2] in ['XY', 'RR']:
...      print aValue[2:]
...  else:
...      print aValue
...      
885442554
TY3485694873
473892711

particularly useful to avoid extensive if, elif, else statements

Re: Remove first 2 characters using if statement

AmyKlug — Sun, 12 Dec 2021 06:42:17 GMT

To emphasize the useage of the "in" list operand consider the following:
>>> bunchOfValues = ['XY885442554', 'TY3485694873', 'RR473892711']
>>> for aValue in bunchOfValues:
...  if aValue[:2] in ['XY', 'RR']:
...      print aValue[2:]
...  else:
...      print aValue
...      
885442554
TY3485694873
473892711
particularly useful to avoid extensive if, elif, else statements

True! Here is the code:

>>> import arcpy
>>> fc = r"H:/Test.gdb/XY_1_1"
>>> cursor = arcpy.da.UpdateCursor(fc, ["NM"])
>>> prefix = ["XY", "RR"]
>>> for row in cursor:
...     row = row[0]
...     if row[:2] in prefix: 
...         cursor.updateRow([row[2:]])
...     else:    
...         print "Name is up-to-date"

Thanks again

Re: Remove first 2 characters using if statement

T__WayneWhitley — Sun, 12 Dec 2021 06:42:20 GMT

That's great Amy!

And just to go a little further because I think I steered you a wee bit wrong in post 4, I said this was 'wrong' but now I don't think so (except you needed the 'if' statement of course):

cursor.updateRow([row[0][2:]])

Actually, I think your code could be shortened to almost what you had originally, see the following, if I can get the formatting preserved from your last post:

>>> import arcpy
>>> fc = r"H:/Test.gdb/XY_1_1"
>>> cursor = arcpy.da.UpdateCursor(fc, ["NM"])
>>> prefix = ["XY", "RR"]
>>> for row in cursor:
...     if row[0][:2] in prefix: 
...         cursor.updateRow([row[0][2:]])
...     else:    
...         print "Name is up-to-date"

...where 'row[0]' is your field object from the list that was previously specified as row = row[0]. Just this line was removed....I didn't test this, but pretty certain it works. I'm just saying you should be able to do it either way.

Hope that makes sense....I'm more accustomed 'seeing' it the other way and actually you should probably make it however is most readable to you (or your workmates, if they see the code).

Enjoy,
Wayne

EDIT:
That's very interesting - and the code I posted may not work! (That's what you get when you post code you have not tested, lol!)

In the Method Overview for the da (data access) module for the UpdateCursor, I only see 'updateRow(row)' where row must be the row object of the cursor -- so if the above code does not work (sorry) or if having trouble, you could try this (I cannot test this da update cursor method at the moment):

>>> import arcpy
>>> fc = r"H:/Test.gdb/XY_1_1"
>>> cursor = arcpy.da.UpdateCursor(fc, ["NM"])
>>> prefix = ["XY", "RR"]
>>> for row in cursor:
...     if row[0][:2] in prefix: 
...         row = row[0][2:]
...         cursor.updateRow(row)
...     else:    
...         print "Name is up-to-date"

Re: Remove first 2 characters using if statement

Anonymous User — Tue, 13 Aug 2013 19:29:42 GMT

If you just want to extract the digits and ignore everything else, why not make it simple:

>>> with arcpy.da.UpdateCursor("Stream_points",['TEST']) as rows: ...     for row in rows: ...         v = row[0] ...         row[0] = ''.join(i for i in v if i.isdigit()) ...         rows.updateRow(row) ...          >>>

This will yield:

2365541
1247884
8965445

EDIT: I should clarify that this removes ALL text and leaves ONLY the digits. If you want to keep other prefixes use Dan or Wayne's method.