How to find prices that occur on the same dates for two sets of stock index prices

I have two sets of stock index returns, both in large 2000ish x 2 column arrays, with dates in the left hand column, and prices in the right. The shorter array only contains 2844 days of data, whereas the longer array contains 2898 days of data.

I am trying to get rid of all days of data that do not occur in both arrays so that I have two equally sized arrays that I can work with ( for example if one array has price data for the 10th of january 2020, but the other does not, I would want to remove that cell).

I am pretty stuck so would really appreciate some help!

Thanks

% An example of the process I would like to achieve is as follows:

shorterarray = [60,70,80 ; '1/1/2020','2/1/2020','4/1/2020']

longerarray = [60,65,75,80 ; '1/1/2020','2/1/2020','3/1/2020','4/1/2020' ]

% since the date 3/1/2020 is only included in the longer array, I would
% want to remove that date from the longer array, along with its
% corresponding price, 75. 


% The larger array has the majority of the values that I would like to
% remove because they are not in the smaller array, but my main attempt 
% seems to keep getting tripped up by the fact that there are some date 
% values in the smaller array that are not in the larger array at all. 

while length(testnikkei)~=length(testnasdaq)
    for i=1:2844
        % this logical part of the for loop works because I have converted
        % the dates into datenum format
        if testnikkei(i,1)==testnasdaq(i,1)
           disp(i);
        elseif testnikkei(i,1)~=testnasdaq(i,1)
            % trying to delete cells from the larger array when they are
            % not equal 
            testnasdaq(i,:)=[];
            break
        end
    end
end

% testnikkei is the shorter array (size 2844), testnasdaq is the longer
% array (size 2898)

Answer 1

[Voss]

shorterarray = {'1/1/2020' 60; '2/1/2020' 70; '4/1/2020' 80}

shorterarray = 3×2 cell array
    {'1/1/2020'}    {[60]}
    {'2/1/2020'}    {[70]}
    {'4/1/2020'}    {[80]}

longerarray = {'1/1/2020' 60; '2/1/2020' 65; '3/1/2020' 75; '4/1/2020' 80}

longerarray = 4×2 cell array
    {'1/1/2020'}    {[60]}
    {'2/1/2020'}    {[65]}
    {'3/1/2020'}    {[75]}
    {'4/1/2020'}    {[80]}

% remove rows from longerarray whose first-column value is not in the first
% column of shorterarray:
longerarray(~ismember(longerarray(:,1),shorterarray(:,1)),:) = []

longerarray = 3×2 cell array
    {'1/1/2020'}    {[60]}
    {'2/1/2020'}    {[65]}
    {'4/1/2020'}    {[80]}