Extract Data from Timetable

Question

Ioannis Tsikriteas 2018-6-2

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https://ww2.mathworks.cn/matlabcentral/answers/403681-extract-data-from-timetable

评论： Ioannis Tsikriteas 2018-6-4

Hi, i have a daytime Matrix and i also have a second timetable of 2 columns (first Time, second Data) of dates from which i want to extract for each daytime of the first Matrix the Data that refers to this Date fromthe second one!

Is there an easy way, without using a for loop, to do so?

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Ioannis Tsikriteas 2018-6-2

编辑：Ioannis Tsikriteas 2018-6-2

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Yes that was the answer!!!! Thanks a lot.

By the way, i have a second problem. I use the addtodate function to add to my datetime 1 year but the problem is that it increases 1 year and 1 second every other row on my daytime matrix. Do you have any idea why this is happening? This is the code i use to add and subtract 5 years to my timetable data

function[y]=add_dates(x,air_temp)
clear y
up=datenum(air_temp.Time(height(air_temp)));
down=datenum(air_temp.Time(1));
x=datenum(x);
for i=1:length(x)
  t=addtodate(x(i,1),-1,'year');
if (t>= down) && (t <= up)
y(i,5)=t;
else
  y(i,5)=0;
end
t=addtodate(x(i,1),-2,'year');
if (t>= down) && (t <= up)
 y(i,4)=t;
 else
  y(i,4)=0;
end
  t=addtodate(x(i,1),-3,'year');
if (t>= down) && (t <= up)
 y(i,3)=t;
 else
 y(i,3)=0;
end
  t=addtodate(x(i,1),-4,'year');
if (t>= down) && (t <= up)
 y(i,2)=t;
 else
 y(i,2)=0;
end
 t=addtodate(x(i,1),-5,'year');
if (t>= down) && (t <= up)
 y(i,1)=t;
 else
  y(i,1)=0;
end
   t=addtodate(x(i,1),1,'year');
if (t>= down) && (t <= up)
y(i,6)=t;
else
  y(i,6)=0;
end
t=addtodate(x(i,1),2,'year');
if (t>= down) && (t <= up)
 y(i,7)=t;
 else
  y(i,7)=0;
end
  t=addtodate(x(i,1),3,'year');
if (t>= down) && (t <= up)
 y(i,8)=t;
 else
 y(i,8)=0;
end
  t=addtodate(x(i,1),4,'year');
if (t>= down) && (t <= up)
 y(i,9)=t;
 else
 y(i,9)=0;
end
 t=addtodate(x(i,1),5,'year');
if(t>= down) && (t <= up)
 y(i,10)=t;
 else
  y(i,10)=0;
end
 i=i+1;
end
end

%

Ioannis Tsikriteas 2018-6-2

编辑：Ioannis Tsikriteas 2018-6-2

在 MATLAB Online 中打开

Paolo it seems the problem is at the conversion from datenum to datetime I changed my code so it does not need to use the addtodate function and to convert to datenum.

Here is my new code and it works

function[y]=add_dates(x,air_temp)
clear y
y=datetime;
up=air_temp.Time(height(air_temp));
down=air_temp.Time(1);
%x=datenum(x);
for i=1:length(x)
  t=datetime(x(i)) - calyears([1]);
  if (t>= down) && (t <= up)
y(i,5)=t;
else
  y(i,5)=NaT;
end
t=datetime(x(i)) - calyears([2]);
if (t>= down) && (t <= up)
 y(i,4)=t;
 else
  y(i,4)=NaT;
end
   t=datetime(x(i)) - calyears([3]);
if (t>= down) && (t <= up)
 y(i,3)=t;
 else
 y(i,3)=NaT;
end
   t=datetime(x(i)) - calyears([4]);
if (t>= down) && (t <= up)
 y(i,2)=t;
 else
 y(i,2)=NaT;
end
 t=datetime(x(i)) - calyears([5]);
if (t>= down) && (t <= up)
 y(i,1)=t;
 else
  y(i,1)=NaT;
end
   t=datetime(x(i)) + calyears([1]);
if (t>= down) && (t <= up)
  y(i,6)=t;
else
  y(i,6)=NaT;
end
 t=datetime(x(i)) + calyears([2]);
if (t>= down) && (t <= up)
 y(i,7)=t;
 else
  y(i,7)=NaT;
end
   t=datetime(x(i)) + calyears([3]);
if (t>= down) && (t <= up)
 y(i,8)=t;
 else
 y(i,8)=NaT;
end
   t=datetime(x(i)) + calyears([4]);
if (t>= down) && (t <= up)
 y(i,9)=t;
 else
 y(i,9)=NaT;
end
  t=datetime(x(i)) + calyears([5]);
if(t>= down) && (t <= up)
 y(i,10)=t;
 else
  y(i,10)=NaT;
end
 i=i+1;
end
end

Peter Perkins 2018-6-4

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Ioannis, I'm pretty sure every loop in your code is unnecessary. For example:

y = NaT(somePreallocationSize);
i = isbetween(x-calyears(1),down,up);
y(i,5) = t(i,5);

I can't really follow everything that's in your code, but that's the idea. This will run MUCH faster and is much simpler to write and maintain.

Ioannis Tsikriteas 2018-6-4

Thank's a lot. You know...i am not as experienced in Matlab as you are. I wanted to add and to substract also to my dates 5 years. Indeed it was slow to execute all these loops but eventually it was a succesful attempt

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Answer 1

Paolo 2018-6-2

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/403681-extract-data-from-timetable#answer_322928

编辑：Paolo 2018-6-2

在 MATLAB Online 中打开

This example will help you.

A datetime matrix:

 daytimemat = datetime(['13/04/2018';'25/04/2018';'28/04/2018'],'Format','dd/MM/yyyy');

A timetable with dates and data.

 tt = timetable(datetime({'13/04/2018';'25/04/2018';'26/04/2018';'28/04/2018'}), [37.3;39.1;42.3;21]);

The following command:

 %Use the index for which tt.Time and daytimemat are equal to find data.
 tt.Var1(tt.Time(daytimemat))

outputs :

3000
1000
0000

which is the data contained in the timetable tt corresponding to the dates in daytimemat array.

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