Insert element in vector

The vector A consist of 223 elements of zeros and other values.

When a value above zero show up, I want to add one/several elements after it, for example -1.

A=[0 0 0 2 0 0 0 3 0 0 1];

becomes

A=[0 0 0 2 -1 0 0 0 3 -1 -1 0 0]

[Sugar Daddy]

https://www.mathworks.com/matlabcentral/answers/48942-insert-element-in-vector

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Answer 1

[Donald Baltus]

It seems you want to conditionally insert values into a vector.

You can insert values into a vector by using concat to reconstruct the original vector with modifications as desired. For example, to just duplicate a vector you could write a function:

function vectorOut = copyVector(vectorIn)
    vectorOut = [];
    for i = 1:numel(vectorIn)
        item = vectorIn(i);
        vectorOut = [vectorOut, [item]];
    end
end

>> copyVector([0 1 2 0 3])

ans =

     0     1     2     0     3
     
>>

You can do something other than just copy each element verbatim however. This function will return the original vector but with each element repeated once:

function vectorOut = repeatVector(vectorIn)
    vectorOut = [];
    for i = 1:numel(vectorIn)
        item = vectorIn(i);
        vectorOut = [vectorOut, [item item]];
    end
end

>> repeatVector([0 1 2 0 3])

ans =

     0     0     1     1     2     2     0     0     3     3

>>

Finally, you can generalize the function by passing a function argument specifying the insertion behavior:

function vectorOut = modifyVector(vectorIn, modifyFunction)
    vectorOut = [];
    for i = 1:numel(vectorIn)
        item = vectorIn(i);
        vectorOut = [vectorOut, modifyFunction(item)];
    end
end

>> modifyVector([0 1 2 0 3], @(x) x+100)

ans =

   100   101   102   100   103

>>

If you write a specialized modify function, you can get the behavior you want:

function replacement = insertIfNotZero(item)
    if item ~= 0
        replacement = [item -1];
    else
        replacement = [item];
    end
end


>> modifyVector([0 1 2 0 3], @insertIfNotZero)

ans =

     0     1    -1     2    -1     0     3    -1

>>

[Rik]

Why are you dynamically growing the array? It seems much more efficient to use other methods, many of which are shown in the thread @Sugar Daddy linked.