Converting dates in time series

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Chris Martin
Chris Martin 2022-3-7
评论： Star Strider 2022-3-8
Dear All, I have a time seris that containts the time vector as :
27-Feb-2007 12:00:00 58.199 -136.64 -0.0048352
28-Feb-2007 12:00:00 58.199 -136.64 -0.0048265
01-Mar-2007 12:00:00 58.199 -136.64 -0.0048853
02-Mar-2007 12:00:00 58.199 -136.64 -0.0050604
03-Mar-2007 12:00:00 58.199 -136.64 -0.0051769
04-Mar-2007 12:00:00 58.199 -136.64 -0.0052122
I need to change the time format of the time column (first column) to decimal year format. I need the time format something like 2007.0123. please help me

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回答（3 个）

Davide Masiello
Davide Masiello 2022-3-7
编辑：Davide Masiello 2022-3-7
Take a look at this
date = '27-Feb-2007 12:00:00';
str = datestr(datenum(date),'yyyy.dd.mm')
str =
'2007.27.02'
And for more info you can take a look at the following webpages
https://uk.mathworks.com/help/matlab/ref/datenum.html
https://uk.mathworks.com/help/matlab/ref/datestr.html
Star Strider
Star Strider 2022-3-7
编辑：Star Strider 2022-3-7
Ran in:
One approach —
M = {'27-Feb-2007 12:00:00' 58.199 -136.64 -0.0048352
'28-Feb-2007 12:00:00' 58.199 -136.64 -0.0048265
'01-Mar-2007 12:00:00' 58.199 -136.64 -0.0048853
'02-Mar-2007 12:00:00' 58.199 -136.64 -0.0050604
'03-Mar-2007 12:00:00' 58.199 -136.64 -0.0051769
'04-Mar-2007 12:00:00' 58.199 -136.64 -0.0052122};
format long
T1 = cell2table(M)
T1 = 6×4 table
M1 M2 M3 M4 ________________________ ______ _______ __________ {'27-Feb-2007 12:00:00'} 58.199 -136.64 -0.0048352 {'28-Feb-2007 12:00:00'} 58.199 -136.64 -0.0048265 {'01-Mar-2007 12:00:00'} 58.199 -136.64 -0.0048853 {'02-Mar-2007 12:00:00'} 58.199 -136.64 -0.0050604 {'03-Mar-2007 12:00:00'} 58.199 -136.64 -0.0051769 {'04-Mar-2007 12:00:00'} 58.199 -136.64 -0.0052122
ddoy = day(datetime(T1.M1),'dayofyear')/day(datetime(year(T1.M1),12,31),'dayofyear');
% T1.M1 = year(datetime(T1.M1)) + ddoy(:,1) % Not Rounded
T1.M1 = year(datetime(T1.M1)) + round(ddoy(:,1), 4) % Round To 4 Decimal Places
T1 = 6×4 table
M1 M2 M3 M4 _________ ______ _______ __________ 2007.1589 58.199 -136.64 -0.0048352 2007.1616 58.199 -136.64 -0.0048265 2007.1644 58.199 -136.64 -0.0048853 2007.1671 58.199 -136.64 -0.0050604 2007.1699 58.199 -136.64 -0.0051769 2007.1726 58.199 -136.64 -0.0052122
I hope that there are easier ways to do this using datetime functions. I looked, however there doesn’t appear to be a format option for this.
EDIT — (7 Mar 2022 at 14:20)
Added round call to ‘ddoy’ display.
.
  2 个评论
Chris Martin
Chris Martin 2022-3-8
does it take account the leap years ?
Star Strider
Star Strider 2022-3-8
The datetime function (and related functions) accounts for leap years, leap seconds, and every other known time variant.

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Peter Perkins
Peter Perkins 2022-3-7
Here's my solution:
>> tt = timetable(rand(6,1),rand(6,1),'RowTimes',datetime(2007,2,27:32,12,0,0))
tt =
6×2 timetable
Time Var1 Var2
____________________ _______ _______
27-Feb-2007 12:00:00 0.14929 0.92926
28-Feb-2007 12:00:00 0.25751 0.34998
01-Mar-2007 12:00:00 0.84072 0.1966
02-Mar-2007 12:00:00 0.25428 0.25108
03-Mar-2007 12:00:00 0.81428 0.61604
04-Mar-2007 12:00:00 0.24352 0.47329
>> lengthOfYear = @(t) caldays(between(dateshift(t,'start','year','current'),dateshift(t,'start','year','next'),'days'))
lengthOfYear =
function_handle with value:
@(t)caldays(between(dateshift(t,'start','year','current'),dateshift(t,'start','year','next'),'days'))
>>
>> tt.DecimalYear = year(tt.Time) + day(tt.Time,'dayofyear')./lengthOfYear(tt.Time)
tt =
6×3 timetable
Time Var1 Var2 DecimalYear
____________________ _______ _______ ___________
27-Feb-2007 12:00:00 0.14929 0.92926 2007.2
28-Feb-2007 12:00:00 0.25751 0.34998 2007.2
01-Mar-2007 12:00:00 0.84072 0.1966 2007.2
02-Mar-2007 12:00:00 0.25428 0.25108 2007.2
03-Mar-2007 12:00:00 0.81428 0.61604 2007.2
04-Mar-2007 12:00:00 0.24352 0.47329 2007.2
SS, I think this is just about what you did, except for putting the length of year calculation in a function.
Chris, unless you need to export these values, I'd think twice about creating them. It's kind of a terrible time representation in which you get poor precision, and even whole days are subject to round-off errors. SS, that kind of answers why there is not a simpler way to do this, but maybe this is a more common format that I'm aware of.

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