Why computer scientists count from zero?
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 midday
>>> at[10:12]
['programming', 'meeting']
Lunch was at 12 ?
>>> at[12]
'lunch'
When is the meeting?
>>> at.index('meeting')
11
ah, OK meeting starts at 11 o'clock
Antje Jones: OK, I understand, 0-based (starting with 0) is useful when working with a time-like sequences 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) which frequently are 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)
Alternatively, some commands offer a switch to 1-based indices
letter=['A','B','C','D','E']
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!
All names and characters in this dialogue are fictitious, but inspired from discussions at:
http://python-history.blogspot.it/2013/10/why-python-uses-0-based-indexing.html
http://exple.tive.org/blarg/2013/10/22/citation-needed/
http://programmers.stackexchange.com/questions/110804/why-are-zero-based-arrays-the-norm