Multiplying by the number of the day of each month in a cell arrays

Hey all,

I have a 1 x 8 cell which includes tables. In each table, there is the date column and the results column. In each row, I want to multiply results values by the number of days in the month from the date column (considering leap and non-leap years).

For example:

date results new_results

---------- ------------- ---------------

1989-01-01 0.2 31 * 0.2 = 6.2

1989-02-01 0.8 30 * 0.8 = 24

. . .

. . .

. . .

2018-12-01 0.4 31*0.4 = 12.4

I read matlab help and tried to use this code:

calculations = arrayfun(@(x) test{x}.results*days(test{x}.date));

But it not working and say not enough inputs.

I attached my data. Any help is highly appreciated.

Thank you !

Answer 1

[Star Strider]

Try this:

D = load('test.mat');
test = D.test;

T1 = test{1};                                           % Select Table #1 From 'test'
[yt,mt,dt] = ymd(T1.date);                              % Return: Year & Month
dim = eomday(yt,mt);                                    % Return: Days In Month
new_results = T1.results .* dim;                        % Create: 'new_results' Variable (Column)new_results’ Variable (Column)
T1.new_results = new_results;                           % Concatenate

producing for example:

Check = T1(1:12,:)

Check =
  12×6 table
    model_name       date       lon    lat    results    new_results
    __________    __________    ___    ___    _______    ___________

    {'ERA5_1'}    1989-01-01    43     40     0.22701      7.0373   
    {'ERA5_1'}    1989-02-01    43     40     0.66383      18.587   
    {'ERA5_1'}    1989-03-01    43     40      1.4266      44.225   
    {'ERA5_1'}    1989-04-01    43     40      1.9511      58.534   
    {'ERA5_1'}    1989-05-01    43     40      1.6575      51.382   
    {'ERA5_1'}    1989-06-01    43     40      1.3122      39.367   
    {'ERA5_1'}    1989-07-01    43     40     0.86207      26.724   
    {'ERA5_1'}    1989-08-01    43     40      0.6105      18.926   
    {'ERA5_1'}    1989-09-01    43     40     0.77049      23.115   
    {'ERA5_1'}    1989-10-01    43     40      2.9392      91.114   
    {'ERA5_1'}    1989-11-01    43     40      3.2634      97.901   
    {'ERA5_1'}    1989-12-01    43     40      0.9547      29.596   

There is an error in the ‘example’ in the posted Question. February has 28 (or 29) days, never 30.

EDIT — (22 Mar 2020 at 14:13)

This can easily be extended to all the tables in ‘test’:

for k = 1:numel(test)
    Tk = test{k};                                       % Select Table From ‘test’
    VarEnd = numel(Tk.Properties.VariableNames)         % Retrieve: ‘VariableNames’
    [yt,mt,dt] = ymd(Tk.date);                          % Return: Year & Month
    DIM = eomday(yt,mt);                                % Return: Days In Month
    new_Val = Tk{:,VarEnd} .* DIM;                      % Create: ‘new_results’ Variable (Column)
    Tk{:,VarEnd+1} = new_Val;                           % Concatenate
    Tk.Properties.VariableNames{VarEnd+1} = ['new_' Tk.Properties.VariableNames{VarEnd}];
    test{k} = Tk;                                       % Save New Table To Previous Cell
end

The complexity arises because the last variable name in ‘test{1}’ is ‘results’ and in the rest it is ‘precip’. This accommodates every table regardless of what the last variable (column) name is.

[BN]

Thank You All. I truly appreciate all your help. In fact, this answer is exactly what I was looking for.

Thank you both again. +1 votes.

[Star Strider]

As always, my pleasure!

Answer 2

[Thiago Henrique Gomes Lobato]

Days will not calculate the days in a specific month, you have to do it manually, so you have to check which years are leap years, which month is which etc. Here is an implementation that will give the result you want

new_results = zeros( size(test{1}.results,1),length(test) );
DaysInMonth = [31,28,31,30,31,30,31,30,31,30,31,30,31]; % Always the same except february

for idxTable = 1:length(test)

% Get numeric values 
M = month(test{idxTable}.date); 
Y = year(test{idxTable}.date);
Days = zeros(size(Y));

% Check which of them are leap years
Leap = mod(Y,400)==1;
Leap =Leap+ ( mod(Y,100)~=0 & mod(Y,4)==0) ;

% Assign to variable Days
for idx=1:12
Days(M==idx) = DaysInMonth(idx);
end

% Add Leap year
Days(M==2 & Leap) = Days(M==2 & Leap)+1;

try
    new_results(:,idxTable) = test{idxTable}.results.*Days;
catch
    new_results(:,idxTable) = test{idxTable}.precip.*Days; % You have different names in the table

end
end