MATLAB: Using logical operator and maintaining array size

logical operator

Say I have x = [ 0 0 1 1 1] and y = [ 4 3 6 6 8]

How do I use logical operator so that I maintain the array size? I want the result to say [ 0 0 6 6 8] – so if it's false then make them zero but keep the rest. I'm trying to avoid if or for loops if possible.

Best Answer

Why logical? its simple multiplication.

>> x.*y
ans =
     0     0     6     6     8

Related Solutions

MATLAB: & operator without if

The & operator is an elementwise operator. Just like the + operator will add corresponding elements of its inputs when given two vectors of the same size:

x = [1 2 3];
y = [4 5 6];
z = x + y % z(1) = x(1) + y(1), z(2) = x(2) + y(2), z(3) = x(3) + y(3)

The & operator will take the and of the corresponding elements of its inputs.

a = [true false true];
b = [true true false];
c = a & b; % c(1) = a(1) & b(1), c(2) = a(2) & b(2), c(3) = a(3) & b(3)

The & operator with two scalars as input returns true if both its inputs are non-zero and false otherwise.

[ true &  true; ... % true
  true & false; ... % false
 false &  true; ... % false
 false & false]     % false

MATLAB: Does the cellfun fails

"...however if I try to apply the same command again as..."

You have failed to take into account that inbetween running these two commands you have changed the data. So while the first cell array only contained scalar numeric (which is a bad way to store numeric data), the second time you call cellfun the cell array now also contains char vectors (lots of 'false', to be precise). Of course when you compare 'false'==1 then the output will be a vector like this:

>> 'false'==1
ans =
     0     0     0     0     0

and that is clearly not a scalar value, so your cellfun usage will fail unless you use 'uni',false and some more complex processing, or wrap the first argument function in any or something similar. Your third example give this error message

Function 'subsindex' is not defined for values of class 'cell'

because when you use the option 'UniformOutput',false then cellfun outputs a cell array, which cannot be used for indexing. So your attempt to use the output as an index will fail.

Here is a simpler approach using a numeric array (which it should be anyway):

>> m = cell2mat(a);
>> id0 = m==0;
>> id1 = m==1;
>> a(id0) = {'false'};
>> a(id1) = {'true'};
>> a
a = 
    'false'    'true'     [    2]    [    3]    [    4]    [    5]    [    6]    [    7]    [    8]    [    9]    [   10]    [   11]
    'true'     'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'
    [    2]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    3]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    4]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    5]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    6]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    7]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    8]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [    9]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [   10]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    [   11]    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'true'     'false'    'false'    'false'

Note that your row and column headers indicate that you should perhaps be using a table, or only storing the actual data (not the headers) in a simple numeric array. Then you could do this task very simply with some basic indexing:

>> c = {'false','true'};
>> b = c(1+m(2:end,2:end))
b = 
    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'false'    'false'    'false'    'false'
    'true'     'true'     'true'     'false'    'false'    'true'     'false'    'true'     'false'    'false'    'false'

Best Answer

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MATLAB: & operator without if

MATLAB: Does the cellfun fails

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