Using ArcGIS Field Calculator and Python Parser to add zeros and ones?

Question

I have a lot of rows of data, and I want to use the field calculator to give a uniform assignment of

0
1
0
1
0
1
... 

but I don't know how to implement it.

Can someone help me?

Answer 1

Use this advanced field calculator expression (Python):

i=0
def switch():
 global i
 i=1-i
 return i
*-------
switch()

Answer 2

As @PolyGeo mentioned, the modulo operator helps you determine whether a number is pair or not. You can check the "Show Codeblock" box in the field calculator and then write a simple function that determines wheter the row is pair or not and adds a 0 or a 1 depending on the condition

def calc(fid):
    if fid % 2 != 0:
        return 0
    else:
        return 1

Then, in the box under you jsut have to call the function using the FID field as an argument.

calc( !FID! )

Note: make sure python is checked as the parser.