[Year 12 SofDev] Records and Arrays

[Guy Flaherty]

Wikipedia uses the term 'element' instead of 'variable' as Adrian suggested. It clarifies this to explain an element can be a value or a variable. Would that be more appropriate? So an array is a collection of elements that are referenced through an index value. Additionally, it seems important that arrays be defined with a reference to using a contiguous block in memory to store the elements.

Guy Flaherty

>>> Steven Bird  19/08/10 9:39 PM >>>
On 19 August 2010 20:53, Janson, Adrian A <
janson.adrian.a at edumail.vic.gov.au> wrote:
> A one dimensional (or 1D) array is a data structure in which variables are
grouped together under the same name...

I see a couple of problems with this definition.  First, an array can group
together things which are not variables, i.e. literals, e.g. in Python:

>>> foo = [1, 1, 2, 3, 5, 8, 13, 21]
>>> bar = ["no", "variables", "here!"]

Second, an array is an array even if it doesn't have a name, e.g. in Python:

>>> my_function(["I", "don't", "have", "a", "name"])
>>> ["indexing", "a", "literal", "array"][2]

> A record is a structure that can be used to group together variables for a
particular purpose.

This definitions shares the first problem above, but it also brings in
something extraneous: "for a particular purpose".  Surely any data structure
serves some particular purpose intended for it by a programmer.

> Indexing the elements of a record is often done via an identifier which is
declared at the same time as the record.

This is true when the record is implemented as an associative array, but not
when it is represented as a tuple.  E.g. in Python:

>>> array_of_tuples = [(1441412050, 'Alice in Wonderland', 'Lewis Carroll'),
...     (1441412341, 'Through the Looking Glass', 'Lewis Carroll')]
>>> print array_of_tuples[1][2]
Lewis Carroll

Here we accessed an element of a record using an integer.  But you're
probably ok here since you said "often", and I agree with that.

-Steven Bird


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Date: 2010-08-19 21:37:47.826
From: sofdev-bounces at edulists.com.au
To: g.flaherty at xavier.vic.edu.au
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