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0-based indices

Why Python uses zero-based indices and not one-based as in Matlab, Mathematica, and R?

Why computer scientists count from zero?

(At) lunch break


Antje Jones: I had a list of letters:
>>> letter=['A','B','C','D','E']
and tried to get the second letter 'B':
>>> letter[2]
'C'
Surprisingly I got a 'C'?!   This is confusing!   A is the 0th letter?!   No one counts like that!

Mike Zero: I agree, for working with objects, 0-based makes no sense. But starting at zero is the way of thinking about time (and data-streams). We don't see the index as an label of an object (for this we use dictionaries), we see the index as a start position of a new interval: a new hour or a new block of data (reading the next 100 letters from a file). We don't 'count' from zero, we simply mean the 'first' element starts at 0.

Let's look to my morning live-stream from midnight (zero) until now:
at=['brr','brr','r','r','r','r','r','r','breakfast','goToWork','programming','meeting','lunch']
   |     |     |   |   |   |   |   |   |           |          |             |         |       |
   0     1     2   3   4   5   6   7   8 o'clock   9         10            11        12   now(end)

What I did between 8 and 10 o'clock?
>>> at[8:10]
['breakfast', 'goToWork']

..and then? What I did from 10 until lunch
>>> at[10:12]
['programming', 'meeting']

Lunch was at 12
>>> at[12]
'lunch'

When is the meeting?
>>> at.index('meeting')
11
ah, OK at 11 o'clock

Antje Jones: OK, I understand, 0-based (starting with 0) is useful when working with a time-like sequence of data. But I need to work with objects: biological samples (1st, 2nd, 3rd, etc.) and 20,000 genes for which starting with 1 is more intuitive: gene[1], gene[2],...

Mike Zero: Unfortunately, it's not possible or at least very confusing to have both 0-based and 1-based indices in the same programming language. Therefore, mathematical languages working with objects (samples) are often 1-based. More general-purpose languages (C++, Java, and Python) typically used to read and process data-streams, are 0-based.

In Python, you can avoid using direct indices in for loops by using in
for element in mylist:
    print(element)


Also, some commands offer a switch to 1-based indices
for i, element in enumerate(letter,1):
    print(i,element)
(1, 'A')
(2, 'B')


And, instead of using lists, you can handle objects by using dictionaries.    


Antje Jones: Thanks a lot!





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