MATLAB: Adding numbers in array in a specific order

digital image processingequalization

Need to create a code for the following statement:

let a=[1 3 5 6 6 7 7 7] , b=[81 122 245 329 656 790 850 1023]

c=[1 1 1 2 3] where c is showing how many times a unique value of a has been repeated e.g. '1' is repeated '1' time, '6' is repeated '2' times and so on.

Now what I need to do is to create d such that if 1st index of c is 1 then assign 1st index value of b to d and if 1st index of c is 2 then assign 1st and 2nd index value of b to d.

In short what I need is d which will have value d=[81 122 245 329+656 790+850+1023].

Will appreciate your help:D

Best Answer

>> [~,~,X] = unique(a);
>> d = accumarray(X(:),b(:))
d =
     81
    122
    245
    985
   2663

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MATLAB: I want to transfer data from a for loop into a vector, i need to use rows of a matrix, every 3rd number(not every 3rd entry) in first column( 2 to 5 repeated numbers for each, tho random). Prob is output length unknown so difficult to prelocate

We can avoid the loop altogether by using the very efficient bsxfun instead:

x = [1,4,7,10,13,16,19,22,25,28,31,34,37,40,43,46,49,52,55,58,61,64,67,70,73,76,79,82,85,88,91,94,97,100,103,106,109,112,115,118,121,124,127,130,133,136,139,142,145,148,151,154,157,160,163,166,169,172,175,178,181,184,187,190,193,196,199,202,205,208,211,214,217,220,223,226,229,232,235,238,241,244,247,250,253,256,259,262,265,268,271,274,277,280,283,286,289,292,295,298,301,304,307,310,313,316,319,322,325,328,331,334,337,340,343,346,349,352,355,358,361,364,367,370,373,376,379,382,385,388,391,394,397,400,403,406,409,412,415,418,421,424,427,430,433,436,439,442,445,448,451,454,457,460,463,466,469,472,475,478,481,484,487,490,493,496,499,502,505,508,511,514,517,520,523,526,529,532,535,538,541,544,547,550,553,556,559,562,565,568,571,574,577,580,583,586,589,592,595,598,601,604,607,610,613,616,619,622,625,628,631,634,637,640,643,646,649,652,655,658,661,664,667,670,673,676,679,682,685,688,691,694,697,700,703,706,709,712,715,718,721,724,727,730,733,736,739,742,745,748];
B(:,2) = 1:6;
B(:,1) = [40,0,106,0,0,487]
idx = any(bsxfun(@eq,B(:,1),x),2);
out = B(idx,:)

which displays this in the command window:

>> Untitled
B =
    40     1
     0     2
   106     3
     0     4
     0     5
   487     6
out =
    40     1
   106     3
   487     6

This is a kind of code vectorization, which is important to learn if you want to use MATLAB efficiently.

MATLAB: How to get vectors of common duplicates in a cell array

>> [~,~,X] = unique(A);
>> [B,Y] = hist(X,1:max(X));
>> C = arrayfun(@(y)find(X==y),Y(B>1),'uni',0);
>> C{:}
ans =
  1  5  6
ans =
  3  4

>> [~,~,X] = unique(A);
>> V = 1:numel(A);
>> C = accumarray(X(:),V(:),[],@(v){v});
>> C(cellfun(@isscalar,C)) = [];
>> C{:}
ans =
  1
  5
  6
ans =
  3
  4

Or a simple loop.

Best Answer

Related Solutions

MATLAB: I want to transfer data from a for loop into a vector, i need to use rows of a matrix, every 3rd number(not every 3rd entry) in first column( 2 to 5 repeated numbers for each, tho random). Prob is output length unknown so difficult to prelocate

MATLAB: How to get vectors of common duplicates in a cell array

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