Code of the day: 2 and 3 dimensional arrays

[Sebastian Gniazdowski <sgniazdowski@xxxxxxxxx>]

Hello,
as Daniel revealed 2-dimensional array may be implemented using single
array if the second dimension – length of row – is fixed. For example,
array[2][4], i.e. two rows of size four, would look like: array=( 11
12 13 14 21 22 23 24 ). If one can agree to not store empty strings
into the array, then quite a normal two-dimensional array usage might
be performed, and the number of rows can grow.

Array here is in a sense of C-arrays, i.e. a rectangle of elements,
not in the sense that every main element of the array holds sub-array
that is independent from other sub-arrays. However, if one will store
into sub-arrays into first empty element, then he can grow that array
– except the number of elements cannot exceed the second dimension –
row size, and that empty string has special meaning – lack of element.

A library that implements helper functions for this, to not do the
index computation all over the code:

https://github.com/psprint/zaccumulator/blob/master/plugins/2array.laccu

The same can be done for 3-dimensional arrays:

https://github.com/psprint/zaccumulator/blob/master/plugins/3array.laccu

When adding a row to the array, it is probably best to use temporary
array, and when it's finished then store it into multi-dimensional
array in one go – to not index on potentially large multi_array:

#################################################
local -a multi_array
zaccu_2arr_format "multi_array" 3 10  # multi_array[3][10]

local -a new_row
new_row[10+1]="END"
new_row[1]="a"
new_row[2]="b"
new_row[3]="c"

zaccu_2arr_get_row_indexes 2 10  # Second row, row_size=10
multi_array[reply[1],reply[2]]=( "${(@)new_row[1,10]}" )

After running the code:
% declare multi_array
multi_array=( '' '' '' '' '' '' '' '' '' '' a b c '' '' '' '' '' '' ''
'' '' '' '' '' '' '' '' '' '' IM_AFTER_END_OF_ARRAY )
#################################################

Of course if multi_array is empty then one would have to store only 3
first elements of new_row. I'll probably add something like to call
zaccu_2arr_get_row_indexes_limited 2 10 3, to get first 3 elements of
row in reply[1],reply[2]. And also some functions that would find
first empty element, return current row usage, etc.

Best regards,
Sebastian Gniazdowski