Find Second Closest Datetime

Hi all,

I have two datetime tables say A and B. I am able to compare A to B and extract the datetimes in A nearest to B with no repetitions. That’s no datetime in A can be selected twice.

Now I want to compare A to B and instead of the nearest in A to B, I want to select or find the second nearest or highest datetime. For example, given the following datetimes, A = 2/1/2016 11:42, 2/1/2016 11:44 and B = 2/1/2016 11:43. The closest datetime comparing A to 2/1/2016 11:43 in B is 2/1/2016 11:42. Now what if I want to select the second highest or second closest/nearest datetime to 2/1/2016 11:43? In this case it will be 2/1/2016 11:44. I want to do this in a loop since A and B contains multiple datetimes. Compare A to B and select the indexes of all second nearest/highest/closest datetime in A to B. And then I will use the indexes to extract row data from another table. I am still learning and I appreciate your help. Thanks!

Answer 1

[Adam Danz]

This is a slight modification from the answer in your previous question.

It uses [B,I] = mink(A,k) to locate the k_th smallest value in array A.

See two lines with the comment " % CHANGED " and one line with the comment " % ADDED " to see how this answer differs from the previous one.

Also note that this can be used instead of the previous one by setting nThClosest to 1.

% Create two arrays of random dates (may contain repeated dates)
dates1 = datetime(2019,1,1)+days(sort(randi(364,1,100)));
dates2 = datetime(2018,12,28)+days(sort(randi(364,1,100)));
% Select the n_th closest date (positive integer)
nThClosest = 2;                     % ADDED
% Loop through the dates in date1
nearestIdx = nan(size(dates1));    % Pre allocation
dates2Temp = dates2;               % Make a temp copy of dates2 for NaT replacement
for i = 1:numel(dates1)
    [~, minKdurr] = mink(abs(dates2Temp - dates1(i)),nThClosest );   % CHANGED
    nearestIdx(i) = minKdurr(end);                                   % CHANGED
    dates2Temp(nearestIdx(i)) = NaT;                        % replace that date with NaT
end
% Sanity check: all of the values in nearestIdx should be unique
assert(numel(unique(nearestIdx))==numel(dates1),'Sanity check failure: unique date matching error.')
% Match the dates (dates1 and dates2 must have same size)
m = [dates1.', dates2(nearestIdx).']

[Curious Mind]

Thank you @Adam Danz for your patience and guidance. This is absolutely nice of you!

[Adam Danz]

Glad I can help!