return value of [ ] for an 'if' or 'for' function

Say I have any function and the input can be input = 123.

For this function, only numbers can work as the input or else the return value should be [ ].

So if i were to have input = 'abc', the return value would need to show [ ].

How can I do this? If the input passes that first test it needs to be able to run the rest of the code.

Here is something i tried, it did not work.

Distance = 'abc'

if Distance = lettersPattern

res = []

end

Additionally, how can i also link the part abvoe to another requisite. If the input is empty to say 'unknown'?

if isempty(cLine)

res = 'unknown'

end

Answer 1

[Akira Agata]

How about the following?

function output = yourFunction(input)

if isempty(input)
  output = 'unknown';
elseif isa(input,'numeric')
  output = input;
else
  output = [];
end

end

[Akira Agata]

Well, in that case the Regular expression will work, like:

function output = yourFunction2(input)

str = regexp(input,'^\d{3}-\d{2}-\d{2}$','match');

if ~isempty(str)
  output = input;
else
  output = [];
end

end

For example:

>> yourFunction2('000-01-00')

ans =

'000-01-00'

>> yourFunction2('000-01-0a')

ans =

[]