concatenating / manipulating matrix based on user input

Question

karan 2011-11-12

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https://ww2.mathworks.cn/matlabcentral/answers/21025-concatenating-manipulating-matrix-based-on-user-input

So below is the matrix which gives me indexes of data sets defined by dates(represented in column 3, column 1 and column 2 are the first index and last index of that data set).

Matrix_dates_present_indexes =

           1        1701           1
        1702        4955           2
        4956        8286           3
        8287       11458           4
       11459       14740           5
       14741       18019           6
       18020       21522           7
       21523       24994           8
       24995       27057           9

I made the above table so i can grab these indexes and get the represeting values.

what i want to achieve is a extracted matrix based on a user input lets say the user wants data analysis of section 1,2,7,8 only from the whole data set.

index_for_calculation = [1, 2, 7, 8]

then how can u get data into a new matrix with concatenated data saying

new_matrix_want = [1:1701 , 1702:4955 , 18020:21522 ,21523:24994 ]

i hope u understand my question...if not i would like to give more calculation..

thanks

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Answer 1

Sven 2011-11-12

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https://ww2.mathworks.cn/matlabcentral/answers/21025-concatenating-manipulating-matrix-based-on-user-input#answer_27737

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Hi Karan, try this:

The setup:

matrix_dates = [           1        1701           1
        1702        4955           2
        4956        8286           3
        8287       11458           4
       11459       14740           5
       14741       18019           6
       18020       21522           7
       21523       24994           8
       24995       27057           9]
inds_to_calc = [1, 2, 7, 8];

The "for-loop" way:

indices_cell = cell(size(inds_to_calc));
for i = 1:length(inds_to_calc)
    from = matrix_dates(inds_to_calc(i),1);
    to = matrix_dates(inds_to_calc(i),2);
    indices_cell{i} = from:to;
end
all_indices = cat(2, indices_cell{:});

Or you could try the sneaky (more difficult to follow) 1-line way:

all_indices = cell2mat(arrayfun(@(from,to)from:to, matrix_dates(inds_to_calc,1), matrix_dates(inds_to_calc,2), 'UniformOutput',false)');

Either way, the answer that you wanted:

new_matrix_want = [1:1701 , 1702:4955 , 18020:21522 ,21523:24994 ]

is in the "all_indices" variable.

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karan 2011-11-12

PERFECT!!!!!

i tried the for-loop structure before but it wasn't storing the data for the 'n' number of inputs ...all it did was give me the last sector of data that i wanted...

But your code above works...

I really appreciate your help...