Indexing list of lists

David C. Fox davidcfox at post.harvard.edu
Thu Sep 18 20:25:19 CEST 2003


Hilde Roth wrote:

>>Like it or not, there are no "different dimensions", just lists of lists 
>>of lists... 
> 
> 
> You are being too litteral. A list of list is like a 2D array from an
> indexing point of view, a list of lists of lists like a 3D array etc.
> E.g., (((1,10),(2,20),(3,30)),((-1,'A'),(-2,'B'),(-3,'C'))) is a  
> 2 x 3 x 2 rectangular data structure and has 3 dimensions. Hence,
> e.g., l[0;2;1] ~ l[0][2][1] = 30

Only if all the sublists are of the same length, which is guaranteed for 
a multi-dimensional array, but not for a list of lists.

What do you expect a[;1] to return if a = [[], [1, 2, 3], [4], 5]?

That's why Numeric has a specific type for multi-dimensional arrays.

David





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