compare variable with different data types

Question

clauper 2023-4-14

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评论： Adam Danz 2023-4-14

I would like to run different lines of code, depending on the value of x. However, x can be string, logical, or numerical.

The example bellow does not work because ismember only accepts string input. Is there another way that can compare x with multiple data types?

x="yes"; % x can be string, logical, or numerical
if ismember(x, {"yes", 1, true})
    
    disp("It is true")
    
elseif ismember(x, {"no", 0, false})
    
    disp("It is false")
end

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Answer 1

Stephen23 2023-4-14

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编辑：Stephen23 2023-4-14

在 MATLAB Online 中打开

Here is a neat approach that also allows case-insensitivity:

x = 'Yes'; % x can be char, string, logical, or numerical
if strcmpi(string(x),"YES")||isequal(x,1)
    disp("It is true")
else
    disp("It is false")
end
It is true
x = true; % x can be char, string, logical, or numerical
if strcmpi(string(x),"YES")||isequal(x,1)
    disp("It is true")
else
    disp("It is false")
end
It is true
x = 0; % x can be char, string, logical, or numerical
if strcmpi(string(x),"YES")||isequal(x,1)
    disp("It is true")
else
    disp("It is false")
end
It is false

With STRNCMPI you can make it also accept partial "Y", "y", "N"; etc.:

x = "y"; % x can be char, string, logical, or numerical
s = string(x);
if strncmpi(s,"YES",strlength(s))||isequal(x,1)
    disp("It is true")
else
    disp("It is false")
end
It is true

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Adam Danz 2023-4-14

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You could even use

if strcmpi(string(x),"YES")||x

One thing I like about validatestring is that in addition to supporting partial matches and case insensitivity, it also casts the input string to the clas specified by the valid string list (char/string) and throws a helpful error message when the input string does not match one of the options.

 x = "yES";
 str = validatestring(x,["yes","no"])
str = "yes"
 
 x = 'what?';
 str = validatestring(x,["yes","no"])
Expected input to match one of these values:

'yes', 'no'

The input, 'what?', did not match any of the valid values.

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Answer 2

Rik 2023-4-14

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编辑：Rik 2023-4-14

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I use the function below. Since loops are fast, I just loop through all the options.

I use this for input validation, so this order of outputs makes most sense for my use. For your use you may consider swapping the output arguments.

function [isLogical,val]=test_if_scalar_logical(val)
%Test if the input is a scalar logical or convertible to it.
% The char and string test are not case sensitive.
% (use the first output to trigger an input error, use the second as the parsed input)
%
%  Allowed values:
% - true or false
% - 1 or 0
% - 'on' or 'off'
% - "on" or "off"
% - matlab.lang.OnOffSwitchState.on or matlab.lang.OnOffSwitchState.off
% - 'enable' or 'disable'
% - 'enabled' or 'disabled'
persistent states
if isempty(states)
    states = {...
        true,false;...
        'true','false';...
        1,0;...
        '1','0';...
        'on','off';...
        'enable','disable';...
        'enabled','disabled'};
    % We don't need string here, as that will be converted to char.
end
% Treat this special case.
if isa(val,'matlab.lang.OnOffSwitchState')
    isLogical = true;val = logical(val);return
end
% Convert a scalar string to char and return an error state for non-scalar strings.
if isa(val,'string')
    if numel(val)~=1,isLogical = false;return
    else            ,val = char(val);
    end
end
% Convert char/string to lower case.
if isa(val,'char'),val = lower(val);end
% Loop through all possible options.
for n=1:size(states,1)
    for m=1:2
        if isequal(val,states{n,m})
            isLogical = true;
            val = states{1,m};
            return
        end
    end
end
% Apparently there wasn't any match, so return the error state.
isLogical = false;
end

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Adam Danz 2023-4-14

You could also define an enumeration class to recognize the options 1|0|true|false|Yes|No.

Rik 2023-4-14

That would be a nice and neat solution, but I'm a freak (which in this case means I want to maintain compatibility with Matlab 6.5 and with Octave), so unfortunately this option is out. But it defenitely deserves an honorable mention.

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Answer 3

Adam Danz 2023-4-14

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Detect if x is a string or character array
Validate the string and convert it to a logical where yes==true
Use a conditional statement to detect if x is true (works for logicals and numerics)

if isstring(x) || ischar(x)
     yesno = validatestring(x,{'yes','no'});
     x = strcmp(yesno,'yes'); 
end
if x
    disp('It is true')
else
    disp('It is false')
end

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Answer 4

Antoni Garcia-Herreros 2023-4-14

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Hello,

You can take a look at the isa function to determine the datatype of x.

Something like this should do the trick:

if isa(x,'char')
    if strcmp(x,'yes')
        disp("It is true")
    else
        disp("It is false")
    end
    
elseif isa(x,'logical')
    if x
        disp("It is true")
    else
        disp("It is false")
    end
    
elseif isa(x,'numeric')
    if x==1;
        disp("It is true")
    else 
        disp("It is false")
    end
end