Count entries per time interval in MATLAB

问题

I'd like to count entries per time interval.

Source dataset nx2

2001-03-23 05:01:33.347,55
2001-03-23 05:01:33.603,62
2001-03-23 05:01:33.977,32
2001-03-23 05:01:34.126,30
...

Example output for group count by second:

2001-03-23 05:01:33.000,3
2001-03-23 05:01:34.000,1
...

回答1:

Here is one way:

% dataset
data = {
  '2001-03-23 05:01:33.347', 55 ;
  '2001-03-23 05:01:33.603', 62 ;
  '2001-03-23 05:01:33.977', 32 ;
  '2001-03-23 05:01:34.126', 30 ;
};

% convert to serial date (ignoring the seconds fraction part)
dt = datenum(data(:,1), 'yyyy-mm-dd HH:MM:SS');

% convert to group indices
[dt,~,ind] = unique(dt);

% count occurences per group
counts = accumarray(ind, cell2mat(data(:,2)), [], @numel);

% construct resulting dataset
X = [cellstr(datestr(dt, 'yyyy-mm-dd HH:MM:SS.FFF')) num2cell(counts)];

The result:

>> X
X = 
    '2001-03-23 05:01:33.000'    [3]
    '2001-03-23 05:01:34.000'    [1]

---

We didn't have to convert to serial date numbers, we could have also done the following:

% treat column as a char matrix
dt = char(data(:,1));
dt = dt(:,1:end-4);   % remove fractions of seconds

% unique entries
[dt,~,ind] = unique(dt, 'rows');

% counting
counts = accumarray(ind, cell2mat(data(:,2)), [], @numel);

% result
X = [cellstr(strcat(dt,'.000')) num2cell(counts)];

来源：https://stackoverflow.com/questions/18816458/count-entries-per-time-interval-in-matlab