base2base

function Z = base2base(varargin)
% Three inputs: origin array, origin base, target base
%   If a base is specified by a number, say b, the digits are [0,1,...,d-1].
% The base can also be directly an array with the digits 
%   Fourth input, optional: how many digits the output should have as a
% minimum (padding with leading zeros, i.e with the first digit)
%   Non-valid digits in origin array are discarded.
%   It works with cell arrays. In this case it gives a matriz in which each
% row is padded with leading zeros if needed

%   If the base is specified as a number, digits are numbers, not
%   characters as in `dec2base` and `base2dec`

ic = iscell(varargin{1});
if ~ic, varargin{1} = varargin(1); end
if numel(varargin{2})>1, ax = varargin{2}; bx=numel(ax); else bx = varargin{2}; ax = 0:bx-1; end
if numel(varargin{3})>1, az = varargin{3}; bz=numel(az); else bz = varargin{3}; az = 0:bz-1; end
Z = cell(size(varargin{1}));
for c = 1:numel(varargin{1})
x = varargin{1}{c}; [valid, x] = ismember(x,ax); x = x(valid)-1;
if ~isempty(x)
    z = NaN(1,ceil(numel(x)*log2(bx)/log2(bz))); done_outer = false;
    n = 0;
    while ~done_outer
        n = n +1;
        x = [0 x(find(x,1):end)];
        y = NaN(size(x)); done_inner = false;
        m = 0;
        while ~done_inner
            m = m + 1;
            t = x(1)*bx+x(2);
            r = mod(t, bz); q = (t-r)/bz;
            y(m) = q; x = [r x(3:end)];
            done_inner = numel(x) < 2;
        end
        y = y(1:m);
        z(n) = r; x = y; done_outer = ~any(x);
    end
    z = z(n:-1:1);
    if numel(varargin)>=4 && numel(z)<varargin{4}, z = [zeros(1,varargin{4}-numel(z)) z]; end
    z = az(z+1);
    Z{c} = z;
end
end
if ~ic, Z = Z{1};
else
    L = max(cellfun(@numel, Z));
    Z = cellfun(@(x) [zeros(1, L-numel(x)) x], Z, 'uniformoutput', false);
    Z = vertcat(Z{:});
end