Why can I not chain logical comparisons in an if statement?

Question

I'm trying to execute a block of code if one of several conditions is met. Again, for clarity, if any of the conditions are true, I'd like for the code to execute (chain of logical ORs).

When I type this code into Matlab:

if strmatch(T,'Sd') || strmatch(T,'SuperDev') || ...
        strmatch(T,'lrnTrialVD') || strmatch(T,'lrnTrialVIS') || ...
        strmatch(T,'lrnTrialTARGET') || strmatch(T,'lrnTrialAUD')

I get this error:

??? Operands to the || and && operators must be convertible to logical scalar values.

Can someone please tell me where I've gone wrong?

/blz

EDIT: I used the wrong function. strcmp is what I meant to use!

You can use strmatch, and even have a cell array for all your strings, but you need to use any around the strmatch call. — Jonas
– Jonas, Commented Mar 20, 2012 at 13:18

Li-aung Yip · Accepted Answer · 2012-03-20 11:22:02Z

3

I believe this is because the return value of strmatch() is an array, not a scalar, and || might not be defined on array arguments. I don't have MATLAB in front of me (only Octave), but does [1, 2, 3] || [4, 5, 6, 7] work for you?

This would look like:

octave-3.2.4.exe:10> T1 = "Sd"
T1 = Sd
octave-3.2.4.exe:11> T2 = "Lollipop"
T2 = Lollipop
octave-3.2.4.exe:12> regexp(T1,"(Sd|SuperDev|lrnTrial(VD|VIS|TARGET|AUD))" )
ans =  1
octave-3.2.4.exe:13> regexp(T2,"(Sd|SuperDev|lrnTrial(VD|VIS|TARGET|AUD))" )
ans = [](1x0)

edited Mar 20, 2012 at 11:22

answered Mar 20, 2012 at 11:14

Li-aung Yip

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3 Comments

Louis Thibault Over a year ago

Indeed! I just realized I meant to use strmcp!

Li-aung Yip Over a year ago

In general, though, even strcmp shouhld only be used when you want to check if a string is exactly the same as one other string. If you want to check if T is one of six allowable strings, use a regexp.

Louis Thibault Over a year ago

@Li-uang Yip: thanks for the regexp tip, it works beautifully!

High Performance Mark · Accepted Answer · 2012-03-20 11:14:12Z

1

strmatch doesn't necessarily return something which can be converted to a logical scalar value. It might, for example, return a vector of match locations which does not convert without further effort on your part. It's all there in the error message and the product documentation, it really is !

answered Mar 20, 2012 at 11:14

High Performance Mark

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2 Comments

Louis Thibault Over a year ago

Oh christ, how embarassing! I meant to use strcmp ...!

High Performance Mark Over a year ago

No need to call me Christ though I appreciate the sentiment.

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