MATLAB Answers

0

Fill gaps using Nan in for loop

Asked by Jaehwi Bong on 19 Sep 2019
Latest activity Commented on by Jaehwi Bong on 20 Sep 2019
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!

  0 Comments

Sign in to comment.

2 Answers

Answer by Stephen Cobeldick on 20 Sep 2019
Edited by Stephen Cobeldick on 20 Sep 2019
 Accepted Answer

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

  1 Comment

Thank you so much!

Sign in to comment.


Answer by Shunichi Kusano on 20 Sep 2019

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

  1 Comment

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);

Sign in to comment.