Extracting time from datetime

Question

Manas Pratap 2021-11-6

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1580244-extracting-time-from-datetime

回答： Alessandro Livi 2024-7-11

采纳的回答： Star Strider

Hi,

How would I extract time from a timestamp? Say for example, I have a table with some 10 rows and say 5 columns.

Column 1 is the datestamp, for ex : 12/01/2000 01:00:00 and Column 2 is say Windspeed 30

so row1 looks like 12/01/2000 01:00:00 30

Let row 2 look like

13/01/2000 01:15:00 45 where 45 is the windspeed.

If I use the hours function, I get back only 01. But when I plot the two data with hours on the x axis, at the same point i get 2 values, which is not what I want. I want to plot two lines (for 12th and 13th) with y axis having the windspeed, and x axis having the hours. So if were to plot for say 10 days, i'd have 10 different lines with the y axis being the windspeed and x axis being the hour. But because Im only getting the "hour", for any windspeed values between 01:00:00 - 02:00:00, it all comes under the hour value of "1". I want it to be continuous.

This is what im getting, if you see the x axis has 0 to 24 values, but if the time is say 00:30, it plots at 0 itself and thats why the ugly graph

I'd want a graph like this

where its in hours and not minutes.

Example of the dataset im working with

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Star Strider 2021-11-7

@Manas Pratap — Please see my Comment.

.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Star Strider 2021-11-6

3
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1580244-extracting-time-from-datetime#answer_825069

在 MATLAB Online 中打开

Try this —

C = {'12/01/2000 01:00:00'   30; '13/01/2000 01:15:00'  45}
C = 2×2 cell array
    {'12/01/2000 01:00:00'}    {[30]}
    {'13/01/2000 01:15:00'}    {[45]}
ct = datetime(C(:,1), 'InputFormat','dd/MM/yyyy HH:mm:ss')
ct = 2×1 datetime array
   12-Jan-2000 01:00:00
   13-Jan-2000 01:15:00
Time = timeofday(ct)
Time = 2×1 duration array
   01:00:00
   01:15:00

.

12 个评论
显示 10更早的评论隐藏 10更早的评论

Star Strider 2021-11-6

在 MATLAB Online 中打开

Try this —

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/791964/sample.csv', 'VariableNamingRule','preserve')

T1 = 40×6 table

Var1 timestamp temperature_site1 humidity_site1 temperature_site2 humidity_site2 ____ ____________________ _________________ ______________ _________________ ______________ 0 {'01-03-2018 00:00'} NaN NaN 23.1 61.6 1 {'01-03-2018 00:30'} 21 68 22.9 61.1 2 {'01-03-2018 01:00'} 20 73 23 61.6 3 {'01-03-2018 01:30'} 20 73 22.9 62.5 4 {'01-03-2018 02:00'} 20 73 22.4 63.4 5 {'01-03-2018 02:30'} 20 70 22 63.8 6 {'01-03-2018 03:00'} 19 78 21.7 64.3 7 {'01-03-2018 03:30'} 19 78 21.5 64.7 8 {'01-03-2018 04:00'} 19 78 21.5 65.2 9 {'01-03-2018 04:30'} 19 78 21.1 66.5 10 {'01-03-2018 05:00'} 18 83 20.9 67.4 11 {'01-03-2018 05:30'} 17 81 20.7 68.2 12 {'01-03-2018 06:00'} 17 84.5 20.6 67.8 13 {'01-03-2018 06:30'} 17 88 20.3 69.1 14 {'01-03-2018 07:00'} 17 88 20.9 70.5 15 {'01-03-2018 07:30'} 17 88 20.3 69.5

T1.timestamp(end)

ans = 1×1 cell array

{'01-03-2018 19:00'}

T1.timestamp = datetime(T1.timestamp, 'InputFormat','dd-MM-yyyy HH:mm', 'Format','dd-MM-yyyy HH:mm')

T1 = 40×6 table

Var1 timestamp temperature_site1 humidity_site1 temperature_site2 humidity_site2 ____ ________________ _________________ ______________ _________________ ______________ 0 01-03-2018 00:00 NaN NaN 23.1 61.6 1 01-03-2018 00:30 21 68 22.9 61.1 2 01-03-2018 01:00 20 73 23 61.6 3 01-03-2018 01:30 20 73 22.9 62.5 4 01-03-2018 02:00 20 73 22.4 63.4 5 01-03-2018 02:30 20 70 22 63.8 6 01-03-2018 03:00 19 78 21.7 64.3 7 01-03-2018 03:30 19 78 21.5 64.7 8 01-03-2018 04:00 19 78 21.5 65.2 9 01-03-2018 04:30 19 78 21.1 66.5 10 01-03-2018 05:00 18 83 20.9 67.4 11 01-03-2018 05:30 17 81 20.7 68.2 12 01-03-2018 06:00 17 84.5 20.6 67.8 13 01-03-2018 06:30 17 88 20.3 69.1 14 01-03-2018 07:00 17 88 20.9 70.5 15 01-03-2018 07:30 17 88 20.3 69.5

T1.TimeOfDay = timeofday(T1.timestamp)

T1 = 40×7 table

Var1 timestamp temperature_site1 humidity_site1 temperature_site2 humidity_site2 TimeOfDay ____ ________________ _________________ ______________ _________________ ______________ _________ 0 01-03-2018 00:00 NaN NaN 23.1 61.6 00:00:00 1 01-03-2018 00:30 21 68 22.9 61.1 00:30:00 2 01-03-2018 01:00 20 73 23 61.6 01:00:00 3 01-03-2018 01:30 20 73 22.9 62.5 01:30:00 4 01-03-2018 02:00 20 73 22.4 63.4 02:00:00 5 01-03-2018 02:30 20 70 22 63.8 02:30:00 6 01-03-2018 03:00 19 78 21.7 64.3 03:00:00 7 01-03-2018 03:30 19 78 21.5 64.7 03:30:00 8 01-03-2018 04:00 19 78 21.5 65.2 04:00:00 9 01-03-2018 04:30 19 78 21.1 66.5 04:30:00 10 01-03-2018 05:00 18 83 20.9 67.4 05:00:00 11 01-03-2018 05:30 17 81 20.7 68.2 05:30:00 12 01-03-2018 06:00 17 84.5 20.6 67.8 06:00:00 13 01-03-2018 06:30 17 88 20.3 69.1 06:30:00 14 01-03-2018 07:00 17 88 20.9 70.5 07:00:00 15 01-03-2018 07:30 17 88 20.3 69.5 07:30:00

vn = T1.Properties.VariableNames;

lgdvars = vn(3:6);

lgdvars = cellfun(@(x)strrep(x,'_','\_'), lgdvars, 'Unif',0); % 'escape' The Underscores

figure

plot(T1.TimeOfDay, T1{:,3}, 'DisplayName',lgdvars{1})

hold on

plot(T1.TimeOfDay, T1{:,4}, 'DisplayName',lgdvars{2})

plot(T1.TimeOfDay, T1{:,5}, 'DisplayName',lgdvars{3})

plot(T1.TimeOfDay, T1{:,6}, 'DisplayName',lgdvars{4})

hold off

grid

legend('Location','best')

figure

yyaxis left

plot(T1.TimeOfDay, T1{:,3}, 'DisplayName',lgdvars{1})

hold on

plot(T1.TimeOfDay, T1{:,5}, 'DisplayName',lgdvars{3})

hold off

ylabel('Temperature (°C)')

yyaxis right

plot(T1.TimeOfDay, T1{:,4}, 'DisplayName',lgdvars{2})

hold on

plot(T1.TimeOfDay, T1{:,6}, 'DisplayName',lgdvars{4})

hold off

ylabel('Humidity (%)')

grid

legend('NumColumns',2, 'Location','northoutside')

There is only one file and it appears to cover only one day. Two plotting options are provided.

.

Manas Pratap 2021-11-14

在 MATLAB Online 中打开

I tried the below. However only 1 value is returned...i need all the rows pertaining to the date so that I can plot it hourwise..

T1 = readtable('weather_data_2sites.csv')
T1.timestamp = datetime(T1.timestamp, 'InputFormat','dd-MM-yyyy HH:mm', 'Format','dd-MM-yyyy HH:mm') 
T1.date = datetime(T1.timestamp, 'InputFormat','dd-MM-yyyy HH:mm', 'Format','dd-MM-yyyy') 
T1.TimeOfDay = timeofday(T1.timestamp)
T1.Properties.VariableNames
T_Mar15 = T1(T1.date == '24-06-2018',:)

Star Strider 2021-11-14

在 MATLAB Online 中打开

This turned out to be a much more difficult problem that I at first thought it would be. The reason is that the data do not have consistent sizes, so plotting them against ‘TimeOfDay’ was not possible. I ended up plotting them as best I could, and then grafting the ‘TimeOfDay’ vector onto the plots using a set call, because that’s the only way I could make it work. I’m not certain how robust the code is, however it appears to work reasonably well for these data.

With that, this is my best effort —

T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/799489/weather_data_2sites1.csv', 'VariableNamingRule','preserve')

T1 = 5780×7 table

Var1 timestamp temperature_site1 humidity_site1 temperature_site2 humidity_site2 Var7 ____ ____________________ _________________ ______________ _________________ ______________ ____________________ 0 {'01-03-2018 00:00'} NaN NaN 23.1 61.6 {'01-01-1970 11:59'} 1 {'01-03-2018 00:30'} 21 68 22.9 61.1 {0×0 char } 2 {'01-03-2018 01:00'} 20 73 23 61.6 {0×0 char } 3 {'01-03-2018 01:30'} 20 73 22.9 62.5 {0×0 char } 4 {'01-03-2018 02:00'} 20 73 22.4 63.4 {0×0 char } 5 {'01-03-2018 02:30'} 20 70 22 63.8 {0×0 char } 6 {'01-03-2018 03:00'} 19 78 21.7 64.3 {0×0 char } 7 {'01-03-2018 03:30'} 19 78 21.5 64.7 {0×0 char } 8 {'01-03-2018 04:00'} 19 78 21.5 65.2 {0×0 char } 9 {'01-03-2018 04:30'} 19 78 21.1 66.5 {0×0 char } 10 {'01-03-2018 05:00'} 18 83 20.9 67.4 {0×0 char } 11 {'01-03-2018 05:30'} 17 81 20.7 68.2 {0×0 char } 12 {'01-03-2018 06:00'} 17 84.5 20.6 67.8 {0×0 char } 13 {'01-03-2018 06:30'} 17 88 20.3 69.1 {0×0 char } 14 {'01-03-2018 07:00'} 17 88 20.9 70.5 {0×0 char } 15 {'01-03-2018 07:30'} 17 88 20.3 69.5 {0×0 char }

T1.timestamp = datetime(T1.timestamp, 'InputFormat','dd-MM-yyyy HH:mm', 'Format','dd-MM-yyyy HH:mm')

T1 = 5780×7 table

Var1 timestamp temperature_site1 humidity_site1 temperature_site2 humidity_site2 Var7 ____ ________________ _________________ ______________ _________________ ______________ ____________________ 0 01-03-2018 00:00 NaN NaN 23.1 61.6 {'01-01-1970 11:59'} 1 01-03-2018 00:30 21 68 22.9 61.1 {0×0 char } 2 01-03-2018 01:00 20 73 23 61.6 {0×0 char } 3 01-03-2018 01:30 20 73 22.9 62.5 {0×0 char } 4 01-03-2018 02:00 20 73 22.4 63.4 {0×0 char } 5 01-03-2018 02:30 20 70 22 63.8 {0×0 char } 6 01-03-2018 03:00 19 78 21.7 64.3 {0×0 char } 7 01-03-2018 03:30 19 78 21.5 64.7 {0×0 char } 8 01-03-2018 04:00 19 78 21.5 65.2 {0×0 char } 9 01-03-2018 04:30 19 78 21.1 66.5 {0×0 char } 10 01-03-2018 05:00 18 83 20.9 67.4 {0×0 char } 11 01-03-2018 05:30 17 81 20.7 68.2 {0×0 char } 12 01-03-2018 06:00 17 84.5 20.6 67.8 {0×0 char } 13 01-03-2018 06:30 17 88 20.3 69.1 {0×0 char } 14 01-03-2018 07:00 17 88 20.9 70.5 {0×0 char } 15 01-03-2018 07:30 17 88 20.3 69.5 {0×0 char }

T1.TimeOfDay = timeofday(T1.timestamp);

T2 = T1(:,[8 3 4 5 6]) % Extract Variables Of Interest To New Table

T2 = 5780×5 table

TimeOfDay temperature_site1 humidity_site1 temperature_site2 humidity_site2 _________ _________________ ______________ _________________ ______________ 00:00:00 NaN NaN 23.1 61.6 00:30:00 21 68 22.9 61.1 01:00:00 20 73 23 61.6 01:30:00 20 73 22.9 62.5 02:00:00 20 73 22.4 63.4 02:30:00 20 70 22 63.8 03:00:00 19 78 21.7 64.3 03:30:00 19 78 21.5 64.7 04:00:00 19 78 21.5 65.2 04:30:00 19 78 21.1 66.5 05:00:00 18 83 20.9 67.4 05:30:00 17 81 20.7 68.2 06:00:00 17 84.5 20.6 67.8 06:30:00 17 88 20.3 69.1 07:00:00 17 88 20.9 70.5 07:30:00 17 88 20.3 69.5

T2 = fillmissing(T2,'nearest');

T2VN = T2.Properties.VariableNames(2:end)

T2VN = 1×4 cell array

{'temperature_site1'} {'humidity_site1'} {'temperature_site2'} {'humidity_site2'}

[TOD,ixs,ixv] = unique(T2.TimeOfDay);

for k = 1:numel(T2VN)

aggvar{:,k} = accumarray(ixv,T2{:,k+1},[],@(x){x});

end

for k1 = 1:numel(aggvar)

figure

hold on

for k2 = 1:numel(aggvar)

plot(aggvar{k1}{k2})

end

hold off

grid

xt = linspace(0, numel(aggvar{1}{1}), numel(aggvar{1}));

set(gca,'XTick',xt, 'XTickLabel',string(TOD))

title(strrep(T2VN{k1},'_','\_'))

legend(compose('Day %d',1:4), 'Location','best')

end

The plots here are constrained and resize themselves to fit the window. They will probably look better when the code is run offline (that I did not do).

Experiment to get the different results, if desired.

.

请先登录，再进行评论。

Answer 2

Alessandro Livi 2024-7-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1580244-extracting-time-from-datetime#answer_1484533

Simple answer for getting time e.g. now but any array works

timeofday(datetime('now')));

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。