Why Python uses zero-based indices and not one-based as in Matlab, Mathematica, and R? Why computer scientists count from zero? (At) lunch breakAntje 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! Persons and dialogue are invented, inspired from discussions at |
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