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# Peter Perkins

### MathWorks

1,059 total contributions since 2011

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get GPS time to calulate time since referencje epoch
Marta, that depends on what you mean by "GPS time". MATLAB doesn't yet have direct support for GPS time, but if all you want is...

2 months ago | 0

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Find the certain amount of values between NaNs and make another variable from these values
There's no need to loop over the 750K elements. Do this on each row x of your data, i.e. loop from 1:50. Try stepping through t...

2 months ago | 0

Finding row number of a variable existing in a table
I have no idea what you mean by "In this case the second column and third row of the table.", but this sounds like what you want...

2 months ago | 0

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Correlating values from a table using a for loop
Not sure why you think a "loop is better". Try this: >> t = table([1;1;1;1;2;2;2;2;2;2],rand(10,1),rand(10,1),'VariableNames',[...

2 months ago | 0

Comparing matrices and filling in the gaps
There are just so many things you can do with joins: >> a = table(["A";"B";"C";"D";"E";"F"]); >> b = table(["B";"D";"F"], [5;1...

2 months ago | 0

Time weighted average after every 60mins
Or put the data in a timetable and use retime(tt,'hourly','mean'). If you need weights, you can write your own aggregation funct...

2 months ago | 0

How can I construct a struct handle from a string?
A scalar struct with a field for each variable that you would have put in the workspace is often useful. It's like a private wor...

2 months ago | 1

Keeping columns names but replacing value for iteration
You are horzcat'ing tables, and table variable names must be unique. But your two tables both have variables named dist1, dist2,...

2 months ago | 1

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Preallocation of a vector of structure
Audric, it seems like dpb understand what you are doing better than I do, but "in which each cell will be a structure of 42 fiel...

2 months ago | 0

convert hourly data to daily sum
Turn your table into a timetable, and use retime: >> hourmelt = table2timetable(hourmelt); >> head(hourmelt) ans = 8×1 tim...

2 months ago | 0

missing/incorrect use of math operators?
Jocelyn, modulo Geoff's concerns, I think your whole loop can be done as x = 200*3*(0:5)'; Vx = (sqrt(Vx_o) - ((k3/2).*x))^2; ...

2 months ago | 0

Matching the size of two matrices based on values of a column
"contains time in a day in decimal form": That would be your problem. Use timetables with datetimes (or maybe durations?), and u...

2 months ago | 1

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How can I fit a mesh plot axis to a vector of time values?
Does this not do what you need? >> d = datetime(2020,11,1:20); >> t = 1:15; >> mesh(d,t,x) Those dates and temps are evenly-...

2 months ago | 0

how do you plot fft of each sensor for both test
Zeshan, you have all your data in a numeric array, t1. I strongly recommend that you convert that to a timetable. Then your plot...

2 months ago | 1

compare datetime with different lengths
SW, if all you want is a plot, there's nothing special you need to do, just plot them. t1 = datetime(2020,11,19) + caldays(0:2:...

2 months ago | 0

Condition for Specific Data collection
Unless you are using a fairly old version of MATLAB, I strognly recommend that you stay away from xlsread, and use readtable or ...

2 months ago | 0

importing data and plotting
In a more recent version of MATLAB, I would suggest to not use importdata. It's old and gives you a result that is hard to work ...

2 months ago | 0

How do I run my MATLAB program through multiple excel files in the folder?
There is. First step: use readmatrix or readtable, stay away from the much older xlsread. Ditto xlswrite. Then use something lik...

2 months ago | 0

How to import an excel file and split a column
The short answer is no. Your timestamps are stored in the spreadsheet as floating point numbers. But why do you need to split ti...

2 months ago | 0

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Consecutive count of values based on multiple conditions
Put your data in a table, and use rowfun with ID as the grouping variable. Write a function that does all the logic you need to ...

2 months ago | 1

Arrayfun with a timetable
timetable1 is not a timetable, and probably not even legal MATLAB code. I'm going to assume you mean that you have an actual tim...

2 months ago | 0

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How to use multiple arguments in matrix
Or >> t = datetime(2020,1,1,0:8759,0,0); >> scale = [repmat(.2,1,6) repmat(.5,1,8) repmat(.2,1,2) repmat(.5,1,7) .2]; >> scal...

2 months ago | 0

Fill missing NaN by 1 in a table value
Not sure what the question is, but based on your title, "fillmissing".

2 months ago | 0

How to read a netcdf file and convert it to time table
Hamed, it's not currently possible to create a timetable that is 3-D (lat-by-lon-by-time). One thing you can do is make a 45*875...

2 months ago | 0

Plotting Multiple Data Streams with Timestamp
CW, if I am undersatand correctly, you are looking for the same kind of chart that stackedplot makes, for multi-rate data. The o...

2 months ago | 0

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How can i plot multiple plots with respect to date in matlab for forecasting problem ?
No reason why something like this plot(datetime(2020,11,18:30),rand(3,13)) should not work.

2 months ago | 0

if it is greater than 75 percent missing data
I think this would be much simpler if you created a timetable by combining the first 6 vars in the table. Actually, I have no id...

2 months ago | 0

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Why do I get identical outputs from a randomized script?
You don't want to use seeds to get independent parallel random number streams. Switch to using one of the generators that is des...

2 months ago | 0