Fill gaps using Nan in for loop

I have a time series with some gaps in it and i want to fill the gaps with NaN in loop.

For example, my data is

data = [0    50;
        1   100;
        2   200;
        3   300;
        5   500;
        6   600;
        7   700;
        10 1000; 
        0    30;
        2    20;
        6    40]

First column and second column refer to time and signal value. But it has 2 objects. (I have thousands objects.). One was begun from 0(first row), the other one was begun 0(9th row). But sometimes it began from 2 or whatever. The solution code should detect the next result when the value of 1st column decreased.

I'd like to change it as a new_data.

new_data = [1   100;
            2   200;
            3   300;
            4   NaN;
            5   500;
            6   600;
            7   700;
            8   NaN;
            9   NaN;
            10 1000;
            0    30;
            1   NaN;
            2    20;
            3   NaN;
            4   Nan;
            5   Nan;
            6    40]
 

How can I make it?

If anyone can help, it would be greatly appreciated.

Thank you!

Answer 1

[Stephen23]

Using two accumarray calls:

>> data = [0,50;1,100;2,200;3,300;5,500;6,600;7,700;10,1000;0,30;2,20;6,40]
data =
      0     50
      1    100
      2    200
      3    300
      5    500
      6    600
      7    700
     10   1000
      0     30
      2     20
      6     40
>> D = diff(data(:,1),1,1);
>> F = @(v){(v(1):v(end)).'};
>> M = [cell2mat(accumarray(cumsum([true;D<0]),data(:,1),[],F)),accumarray(cumsum([1;max(1,D)]),data(:,2),[],[],NaN)]
M =
      0     50
      1    100
      2    200
      3    300
      4    NaN
      5    500
      6    600
      7    700
      8    NaN
      9    NaN
     10   1000
      0     30
      1    NaN
      2     20
      3    NaN
      4    NaN
      5    NaN
      6     40

[Jaehwi Bong]

Thank you so much!

Answer 2

[Shunichi Kusano]

Hi Jaehwi,

I wrote code. hope this helps.

data = [0 50; 1 100; 2 200; 3 300; 5 500; 6 600; 7 700; 10 1000; 0 30; 2 20; 6 40;];

% find where the value decreases
decreaseIndex = find(diff(data(:,1)) < 0);
% new object begin with decreasing the value
objectBeginIndex = [1, decreaseIndex+1];
%% loop for each objects
objectsNum = length(objectBeginIndex);
fullset = [0:10]';
fulldata = NaN(11*(objectsNum-1), 2); % up to the second last
fulldata(:,1) = repmat(fullset, objectsNum-1, 1);
for i = 1:objectsNum
    if ~(i == objectsNum)
        tempdata = data(objectBeginIndex(i):objectBeginIndex(i+1)-1,:); % extract single object
        existDataIndex = find(ismember(fullset, tempdata(:,1))); % find where the data exist
        fulldata((i-1)*11+existDataIndex, 2) = tempdata(:,2); % place the data
    else % if i is last, up to existing number, not to 10.
        tempdata = data(objectBeginIndex(i):end,:);
        maxi = tempdata(end,1);
        existDataIndex = find(ismember([0:maxi]', tempdata(:,1)));
        lastdata = [[0:maxi]', NaN(maxi+1, 1)]; % up to the second last
        lastdata(existDataIndex,2) = tempdata(:,2);
        fulldata = [fulldata; lastdata];
    end
end

[Jaehwi Bong]

Thank you Shunichi!

I'm trying with a data that have 3 objects. But it keep complaining at the line " repmat". I've revised some line to use it. Do you mind this code?

data2 = [0 50; 1 100; 2 200; 3 300; 5 500; 6 600; 7 700; 10 1000; 0 30; 2 20; 6 40; 0 20; 1 10; 5 50;];
% find where the value decreases
decreaseIndex2 = find(diff(data2(:,1)) < 0);
decreaseIndex = zeros(length(decreaseIndex2)+1,1);
decreaseIndex(2:end) = decreaseIndex2(1:end);
decreaseIndex(1) = 0;

% new object begin with decreasing the value
for k = 1:length(decreaseIndex)
objectBeginIndex(k,1) = decreaseIndex(k)+1;
end
%% loop for each objects
objectsNum = length(objectBeginIndex);
fullset = [0:length(data2)]';
fulldata = NaN(length(data2)*(objectsNum-1), 2);