# How to convert daily data to monthly?

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Mohammad on 5 Dec 2012
Answered: ABHILASH SINGH on 13 Mar 2020
I have huge number of precipitation daily data in a column (say for 60 years) for 400 meteorological stations. Now I need to convert it to monthly. How can I do that? thanks.

per isakson on 5 Dec 2012
Months have 28, 29, 30 or 31 days, which makes it a bit tricky.
Do you have a table with
date, value
rather than just a column?
Does the length of the months matter?
Mohammad on 5 Dec 2012
my data format is Year Month Day data
that is in 4 column. Length of month is always 30. Does it help for providing your answer? thanks.

Andrei Bobrov on 5 Dec 2012
Edited: Andrei Bobrov on 5 Dec 2012
one way
M - your data matrix with 4 columns < Year Month Day data > - double type
[a,~,c] = unique(M(:,1:2),'rows');
out = [a, accumarray(c,M(:,4),[],@mean)];

Chad Greene on 5 Nov 2014
downsample_ts can do this by
precip_monthlymean = downsample_ts(precip_daily,t_daily);

ABDULLA RAHIL on 25 Aug 2016
Hi Chad I tried to use this equation but i couldn't i have a daily data and want to have monthly data
Chad Greene on 31 Aug 2016
My mistake--
precip_monthlymean = downsample_ts(precip_daily,t_daily,'monthly','mean');

Babak on 5 Dec 2012
Every 30 data rows, I would average them out and save it in 1 row.This way, 30 days shrinks down to 1 data (a month). Or another way, you can simply delete 29 data rows and keep only one from every 30 data rows.

Mohammad on 5 Dec 2012
Thanks. But please provide answer through matlab function.
Babak on 5 Dec 2012
you need to write what your variables are and we would know which format they are... I mean what type they are for example, string? double, or cell? moreover they are all in a matrix or a cell or how you ahev sorted them..

per isakson on 5 Dec 2012
Edited: per isakson on 5 Dec 2012
Given thirty days in every month try this
daily_val = rand( 30*12, 1 );
daily_val = reshape( daily_val, 30, [] );
monthly_val = sum( daily_val, 1 );
here I assume that the first value in daily_val is the first value of a month. This is intended as a start.