[Tutor] Extracting bits from an array

[Michael Selik]

> On Apr 29, 2016, at 1:15 PM, Colin Ross <colin.ross.dal at gmail.com> wrote:
> 
> Hello,
> 
> I have an array that takes on the following form:
> 
> x = [1000,1001,1011,1111]
> 
> The array elements are meant to be binary representation of integers.
> 
> Goal: Access array elements and extract the first two bits.
> 
> e.g. Final result would look something like this:
> 
> x_new = [10,10,10,11]
> 
> What I have tried:
> 
> data_indices = range(4)      #  Set up array of values to loop over
> 
> for idx in data_indices:
>     f = x[idx]                          # Index into array of x values

Instead of looping over a range of indices, you should loop over the data itself.

    for number in x:
        s = bin(number)
        print s

>     f_idx = f[:2]                      # Extract first two elements

You couldn't slice an integer. First convert to the binary representation in string form. You can strip off the prefix if you just want the digits.

    s = bin(number).lstrip('0b')

Then you can slice off the first two digits if you want. Remember, it's a str of digits, not a number.

>     print f_idx
> 
> I then receive the following error:
> 
> IndexError: invalid index to scalar variable.
> 
> Any help with accomplishing my outline dgoal would be greatly appreciated.
> 
> Thank you.
> 
> Colin
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