Extract values from a cell based on dates

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Manuel Flores 2018-10-7

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编辑： jonas 2018-10-9

Hi all,

I have data in 6 separate cells (A, B, C, D, E, F), all which are 365x1. One of these cells (A) contains dates as 'datenum' for a whole 12 months. My question is how can I call/pull/extract data from these cells based on date requirements and get an average. i.e. all of the values on the 10th for each month.

Would it be best to use stack and place them all as a table? I don't have any code for this yet as I don't know where to begin.

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Manuel Flores 2018-10-8

Sorry probably be better if I explain it this way. I have 6 cells that are 365x1 in size. Dates (in datenum), Max_Temp, Min_Temp, pressure, Humidity, speed, and Rainfall, which were all imported from 12 monthly excel files. I would like to create a loop or count I guess (not really sure as I'm still new) to place the first 28 days worth of data in a month as a column and store it in a separate cell/matrix, for Max_Temp only.

I would then like to add a 2nd column to this cell or matrix with the first 28 days of data from the following month and so on until I end up with a 28 x 12 cell. Someone one at my work suggested using a count inside a loop so that it only records from the 1st to 28th of each month and skip the rest of the days. i.e 29th, 30th, 31st.

The reason I want the information like this is so that I can do the average value of all the 1st days of the month (since they will be in a row), the 2nd's 3rd's and so on and end up with a cell that's 28x1 of the averages row values.

Hope this is clearer.

P.S. numeric data that's inside the arrays doesn't not matter for this explanation. The key thing is the dates so it knows when to skip the values or not.

jonas 2018-10-8

As was suggested several times already, what you want is a timetable and retime. If you want to calculate some statistics based on the "day of month", then I would suggest using the day of month as a grouping variable. This is easy if you first convert your data to datetime format, which you should do anyway.

Manuel Flores 2018-10-8

Thanks everyone I'm taking the suggestions mentioned and importing it as a table.

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Answer 1

jonas 2018-10-8

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https://ww2.mathworks.cn/matlabcentral/answers/422607-extract-values-from-a-cell-based-on-dates#answer_340312

编辑：jonas 2018-10-8

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Here's another approach

%%Dummy dataset
Date = datetime('2000-01-01')+days(0:364);
Date.Format = 'dd/MMM/yyyy';
Data = rand(numel(Date),5);
%%Data to timetable
TT = timetable(Date',day(Date)',Data)
TT = splitvars(TT)
TT.Properties.VariableNames = {'DayOfMonth','C1','C2','C3','C4','C5'}

TT =

366×6 timetable
       Time        DayOfMonth       C1            C2            C3           C4           C5    
    ___________    __________    _________    __________    __________    _________    _________
    01/Jan/2000         1          0.83516       0.64556       0.79434      0.73071     0.068773
    02/Jan/2000         2          0.11948       0.47084       0.92745      0.75217      0.19456
    03/Jan/2000         3          0.76848       0.28703       0.54273      0.59603      0.94978
    ...

Continuing...

%%Mean, std and max with DayOfMonth as grouping variable
[s1,s2,s3] = grpstats(TT.Variables,TT.DayOfMonth,{'mean','std','max'})
%%Monthly average using retime
TT2 = retime(TT,'monthly','mean')

s1, s2 and s3 are matrices with 31 rows representing the selected statistics for each day of the month.

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Manuel Flores 2018-10-9

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Hey gents I have another question.

I have a code like this where I pull the data based on those 4 dates. That works, so no problem there.

% Pull the Temperature from the design dates.
Tr = {'2017-07-01','2017-07-02','2017-08-01','2017-08-02'};
Tj = TT_all(Tr,2);

Now I'm wondering how to do the same for 28 day for every month over 12 months. Obviously it's not like this.

Tr_all = {'2017-07-01:2017-07-28','2017-08-02:2017-08-28','2017-09-01:2017-09-28'}...
    {'2017-10-01:2017-10-28','2017-11-01:2017-11-28','2017-12-01:2017-12-28'}...
    {'2018-01-01:2011-01-28','2018-02-01:2011-02-28','2018-03-01:2011-03-28'}...
    {'2018-04-01:2011-04-28','2018-05-01:2011-05-28','2018-06-01:2011-06-28'};

can you point me in the right direction please. Thanks

jonas 2018-10-9

编辑：jonas 2018-10-9

在 MATLAB Online 中打开

Easier would be

TT(day(TT.Time)==28,:)

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Extract values from a cell based on dates

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Extract values from a cell based on dates

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