CODEWITHSUNDEEP
matlab
user3040220
user3040220

Reputation: 11

how do I combine some elements into one element of a row matrix

I need to combine some elements into one element of a row matrix in MATLAB. For example, my matrix is [1 2 3 4 5 6 7 8]. I want to transform the matrix like [1234 5678]. Please help me do this.

Upvotes: 1

Views: 1445

Answers (4)

chappjc
chappjc

Reputation: 30579

Consider the following anonymous function for a generalized numeric solution for combining single digits:

combineDigits = @(x) x*(10.^(length(x)-1:-1:0)).';

Each element of x must be on [0,9] (i.e. single digits). For your example input:

>> x = [1 2 3 4 5 6 7 8]
x =
     1     2     3     4     5     6     7     8
>> x1 = x(1:4); x2 = x(5:end);
>> combineDigits(x1)
ans =
        1234
>> combineDigits(x2)
ans =
        5678
>>

The anonymous function combinedDigits can be applied with any general utility function, such as cellfun, to process blocks of data. For example, consider the 2x8 matrix M of digits, partitioned into a 2x2 cell array of 1x4 digit arrays:

>> M = randi(9,2,8)
M =
     4     8     6     8     7     7     6     7
     9     9     1     9     7     4     2     1
>> Mpartitioned = mat2cell(M,[1 1],[4 4]) % specify ANY valid partitioning here
Mpartitioned = 
    [1x4 double]    [1x4 double]
    [1x4 double]    [1x4 double]
>> Mcompacted = cellfun(combineDigits,Mpartitioned)
ans =
        4868        7767
        9919        7421

Upvotes: 3

Bruce Dean
Bruce Dean

Reputation: 2828

First define your values in a numeric array:

a = [1 2 3 4 5 6 7 8];

Next convert to a string:

b = num2str(a);

Now remove all the spaces:

b(find(b == ' ')) = '';

Insert an empty space in the middle and then convert back to a numeric array (I think this is what you want(?)):

c = str2num([b(1:4),' ',b(5:end)]);

So that 

>> c(1)

ans =

        1234

>> c(2)

ans =

        5678

Edit: Added 'end' to cover an arbitrary range.

Upvotes: 1

MrAzzaman
MrAzzaman

Reputation: 4768

It depends. If you can guarantee that your row will always be a multiple of 4, you could do the following:

reshape(sum(bsxfun(@times,reshape(Q',4,[])',[1000,100,10,1]),2),[],size(Q,1))';

What this does is reshape the matrix like so:

[1 2 3 4 5 6 7 8     ->    [1 2 3 4
 8 7 6 5 4 3 2 1]           5 6 7 8
                            8 7 6 5
                            4 3 2 1]

We then multiple each row by [1000,100,10,1] and sum each row:

[1 2 3 4          [1000 200 30 4         [1234
 5 6 7 8    ->     5000 600 70 8   ->     5678
 8 7 6 5           8000 700 60 5          8765
 4 3 2 1]          4000 300 20 1]         4321]

Finally we reshape the matrix again to get back to the original shape.

[1234         [1234 5678
 5678   ->     8765 4321]
 8765          
 4321]

Upvotes: 1

Autonomous
Autonomous

Reputation: 9075

You can do it as following:

a=[1 2 3 4 5 6 7 8];
vec1=a(1:4)  %put a suitable number here
vec1=num2str(vec1);
vec1(ismember(vec1,' ')) = [];
vec1=str2double(vec1);

Similarly, perform the above sequence of operation on the latter half of the vector and simply concatenate them in the final vector.

Note: This solution works only for a row vector as you mentioned in the question (you mentioned row matrix, but I assume this is what you meant).

Upvotes: 1

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