# Return to Answer

3 added 92 characters in body

# Octave, 34 bytes

@(s)mod(nnz(~(s'-'aeiouAEIOU')),2)

s'-'aeiouAEIOU'    % Creates a 2D-matrix where each of the odd letters are
% subtracted from the string s
~(s'-'aeiouAEIOU') % Negates that array, so the all zero elements become 1
nnz( .... )        % Counts all the non-zero elements (the odd letters)
mod(nnz( ....),2   % Takes this sum modulus 2

This is 6 bytes shorter than the traditional approach using ismember, @(s)mod(sum(ismember(s,'aeiouAEIOU')),2), and two bytes shorter than the regex approach: @(s)mod(nnz(regexpi(s,'[aeiou]')),2).

# Octave, 34 bytes

@(s)mod(nnz(~(s'-'aeiouAEIOU')),2)

s'-'aeiouAEIOU'    % Creates a 2D-matrix where each of the odd letters are
% subtracted from the string s
~(s'-'aeiouAEIOU') % Negates that array, so the all zero elements become 1
nnz( .... )        % Counts all the non-zero elements (the odd letters)
mod(nnz( ....),2   % Takes this sum modulus 2

This is 6 bytes shorter than the traditional approach using ismember.

# Octave, 34 bytes

@(s)mod(nnz(~(s'-'aeiouAEIOU')),2)

s'-'aeiouAEIOU'    % Creates a 2D-matrix where each of the odd letters are
% subtracted from the string s
~(s'-'aeiouAEIOU') % Negates that array, so the all zero elements become 1
nnz( .... )        % Counts all the non-zero elements (the odd letters)
mod(nnz( ....),2   % Takes this sum modulus 2

This is 6 bytes shorter than the traditional approach using ismember, @(s)mod(sum(ismember(s,'aeiouAEIOU')),2), and two bytes shorter than the regex approach: @(s)mod(nnz(regexpi(s,'[aeiou]')),2).

2 added 388 characters in body

# Octave, 34 bytes

@(s)mod(nnz(~(s'-'aeiouAEIOU')),2)

s'-'aeiouAEIOU'    % Creates a 2D-matrix where each of the odd letters are
% subtracted from the string s
~(s'-'aeiouAEIOU') % Negates that array, so the all zero elements become 1
nnz( .... )        % Counts all the non-zero elements (the odd letters)
mod(nnz( ....),2   % Takes this sum modulus 2

This is 6 bytes shorter than the traditional approach using ismember.

# Octave, 34 bytes

@(s)mod(nnz(~(s'-'aeiouAEIOU')),2)

# Octave, 34 bytes

@(s)mod(nnz(~(s'-'aeiouAEIOU')),2)

s'-'aeiouAEIOU'    % Creates a 2D-matrix where each of the odd letters are
% subtracted from the string s
~(s'-'aeiouAEIOU') % Negates that array, so the all zero elements become 1
nnz( .... )        % Counts all the non-zero elements (the odd letters)
mod(nnz( ....),2   % Takes this sum modulus 2

This is 6 bytes shorter than the traditional approach using ismember.

1

# Octave, 34 bytes

@(s)mod(nnz(~(s'-'aeiouAEIOU')),2)