Matlab: non-integers or numbers below 1 as indices; numbers as field names-CodePudding

Matlab has limitations in terms of how things can be numbered/indexed:

Arrays and cell arrays require indices that are natural numbers (with exceptions that are discouraged and not more general).
Field names of structure arrays can only be strings that start with a letter and are followed by letters/digits/underscores.

However, it might be normal to number certain things using zero or negative numbers or non-integer numbers.

For example, storing more and more so-called spherical harmonics requires increasingly negative "indices".

Scaling and shifting those "indices" such that they are natural numbers, i.e. valid (cell-)array indices, has disadvantages (smaller negative indices or finer non-integer indices might appear later, requiring a recomputation of the scale or shift parameters and adjustment of the entire data structure; understanding the resulting data structure requires knowing the scale and shift parameters and requires "mental math" while looking at the data).

Is there a way without these disadvantages?

CodePudding user response：

containers.Map might achieve what you want. Apparently it can store any objects as values. That seems to be undocumented.

CodePudding user response：

Numbers can be turned into valid field names for structure arrays for example using this function:

% Field names of Matlab structures:
%  - can't start with a digit, so we prepend 'number_',
%  - can't contain '-', so we replace it by 'minus',
%  - can't contain ' ', so we replace it by 'plus' (for numbers such as -1e 20),
%  - can't contain '.', so we replace it by 'point'.
% For example, the number -0.5 turns into the string 'number_minus0point5'.
num2fieldname = @(x)(['number_' replace(replace(replace(num2str(x),'-','minus'),'.','point'),' ','plus')]);

For example, num2fieldname(-1.5e 20) yields 'number_minus1point5eplus20'.

To use them as field names, here for example using the "index" (2,-1):

mystructure.(num2fieldname(2)).(num2fieldname(-1)) = myobject

It won't work if rounding settings for num2str change.