Spread monthly data into days

2021 9 24
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更新时间：2021 9 27
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Hello,
I am new to Matlab and I am trying to spread monthly data into a table that is indexed daily. For example:
Date Data
01/1982 0.15
02/1982 -0.02
03/1982 -0.05
What I would like to achieve...
Date Data
1/1/1982 0.15
1/2/1982 0.15
1/3/1982 0.15
1/4/1982 0.15
....
1/31/1982 0.15
2/1/1982 -0.02
2/2/1982 -0.02
2/3/1982 -0.02
2/4/1982 -0.02
I other words, I am trying to convert a table with 240 rows (20 years in months) to one with 7300 rows (20 years in days).
Is this easily doable in matlab? Greatly appreciate any advice.

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 采纳的回答

Kelly Kearney
Kelly Kearney 2021-9-25

2 个投票

One way to do the expansion... convert your monthly dates to the first of each month, then use dateshift to check which month each of your days match:
% Some placeholder data... you'll have to read your tables as appropriate
tmon = datetime(1982, 1:3, 1);
ymon = [0.15 -0.02 -0.05];
tday = datetime(1982,1,1) + days(0:89);
% Match up days to months
[~,loc] = ismember(dateshift(tday, 'start', 'month'), tmon);
yday = ymon(loc);

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Ajay Gupta
Ajay Gupta 2021-9-26
Thank you! It worked but now I have to complicate the problem.
The dateshift method you showed worked for one column of data, but I actually have 1000 columns in my data. I tried just calling the 240x1000 array into the ymon variable and it worked, but only for the first column (output is 1x7300 not 1000x7300 as I was expecting). Is there a quick way to revise this code to have it read all 1000 columns and make the shifted dataset?
Thanks again. This was very helpful.
Kelly Kearney
Kelly Kearney 2021-9-27
Can you clarify how your data is stored? Is it in an external file?
Ajay Gupta
Ajay Gupta 2021-9-27
It is not external. Its an array created by my code. (241x1000 double) trying to get to 7300x1000 double.
I think I was able to resolve by adding:
yday = zeros(7300,1000);
yday(:,:) = ymon(loc,:);
Does this make sense?
Thanks again!

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更多回答（1 个）

1 个投票

You can import your data and easily convert them as you need using importdata() - see help DOC and convert date data into numbers using datenum() - see help DOC
Good luck

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