Checking the variable for specific string

Question

Ravikumar Mevada 2019-7-31

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/474272-checking-the-variable-for-specific-string

编辑： Adam Danz 2019-7-31

Very new to Matlab. I need to give 'high' or 'low' in one function's input as shown below. How can I make sure that the variable only accept 'high' or 'low'? If anything else, then there will be an error like 'filter type error'.

Using code bellow, gives error even with 'high' and 'low' input.

Thanks!

function [Y] = butter2filtfilt(x, Fs, Fcutoff, Type) 
if Type~= "high" || Type~= "low"
    error ('Filter type error')
end
end
>> LF = butter2filtfilt(ecg, 257, 0.15, 'low');
Error using butter2filtfilt (line 6)
Filter type error

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Steven Lord 2019-7-31

You've received a couple alternative solutions, but as an explanation for why this doesn't work that if statement is equivalent to "If type is not equal to 'high' or type is not equal to 'low', throw an error".

So what if type is equal to 'high'? The "type is not equal to 'high'" portion of that sentence is false, but the "type is not equal to 'low'" portion is true. Since the condition is false or true, the if is satisfied and so you throw an error.

The same holds if type is equal to 'low', just in reverse order. The first portion is true and the second portion is false.

You want to error if type is not equal to 'high' and type is not equal to 'low', not if one or the other is true.

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Answer 1

Alex Mcaulley 2019-7-31

3
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/474272-checking-the-variable-for-specific-string#answer_385607

function [Y] = butter2filtfilt(x, Fs, Fcutoff, Type) 
if ~ismember(Type,{'high','low'})
    error ('Filter type error')
end
end    

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madhan ravi 2019-7-31

"How can I make sure that the variable only accept 'high' or 'low'? If anything else, then there will be an error like 'filter type error'. "

Adam Danz 2019-7-31

编辑：Adam Danz 2019-7-31

That doesn't mean the user wants to go against typical matlab syntax and force case sensitive input strings on what appears to be a binary flag.

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Answer 2

Adam Danz 2019-7-31

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/474272-checking-the-variable-for-specific-string#answer_385608

编辑：Adam Danz 2019-7-31

This solution uses strcmpi() which which compares strings, allowing for case insensitivity so "High" or "LOW" won't cause an error. When there is an error, it provides the "Type" string that caused the error.

function [Y] = butter2filtfilt(x, Fs, Fcutoff, Type) 
     options = ["high", "low"];  
     if ~any(strcmpi(Type, options))
         error('Filter type error. ''%s'' not recognized.', Type)
     end
end