Countering error while using interp1 function

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Hi,
I am using the code below but getting the error and can not make sense of that error can anyone help please: Attached are the files I am working with.Basically, I am trying to use the time stamps available in both files attached and find the common timestamps for both velocity and head data hence plot them for visualization but I think the size of the both files are different that's why error occuring?
Code:
close all; clear all; clc;
% read data into tables
Udat = readtable('F:\3-PIV_Experimental_Data\Outlet_110\Data_LaserSheet_D\Data_PIV\5-AverageFilter_VelocitiesExtration\Point_Velocities\Uy\TimeStamps_Uy.xlsx');
Hdat = readtable('F:\3-PIV_Experimental_Data\Outlet_110\Data_LaserSheet_D\Data_Head\Data_Raw\Head_Timestamps.xlsx');
% assign variables
tu = datetime(Udat.TimeStamp); % convert to datetime array
u = Udat.Uy
th = datetime(Hdat.TimeStamp);% convert to datetime array
h = Hdat.Head_mm_; % Matlab converts original heading Head(mm) to this legal variable name
% interpolate values for head at times to match those where we have
% velocity data
hq = interp1(th,h,tu);
% plot the results
plot(u,hq,'-o')
Error:
Error using datetime (line 597)
Numeric input data must be a matrix with three or six columns, or else three, six, or seven separate numeric arrays. You can also create datetimes from a
single numeric array using the 'ConvertFrom' parameter.
Error in headvelocitygraph (line 10)
th = datetime(Hdat.TimeStamp);% convert to datetime array

Accepted Answer

John D'Errico
John D'Errico on 13 Mar 2022
Edited: John D'Errico on 13 Mar 2022
Your problem is NOT in interp1. It is in the incorrect use of datetime. Read the error message:
Error using datetime (line 597)
Numeric input data must be a matrix with three or six columns, or else three, six, or seven separate numeric arrays. You can also create datetimes from a
single numeric array using the 'ConvertFrom' parameter.
  3 Comments
Peter Perkins
Peter Perkins on 14 Mar 2022
These two files have what appears to be times of day, or more generally, elapsed times. But the two files are apparently formatted completely differently, because readtable reads the timestamps in one as numeric, in the other as text. Neither is ideal; a properly formatted spreadsheet should cause readtable to read them in as timestamps. Anyway:
>> t1 = readtable("Head_Timestamps.xlsx");
Warning: Column headers from the file were modified to make them valid MATLAB identifiers before creating variable names for the table. The original column headers are saved in the VariableDescriptions property.
Set 'VariableNamingRule' to 'preserve' to use the original column headers as table variable names.
>> head(t1)
TimeStamp Head_mm_
_________ ________
0.56369 0
0.5637 1.2
0.56372 1.2
0.56373 0.7
0.56374 0.8
[snip]
>> t2 = readtable("TimeStamps_Uy.xlsx");
>> head(t2)
TimeStamp Uy
____________ _________
{'13:32:04'} 0.0023132
{'13:33:09'} 0.068063
{'13:33:42'} 0.056888
{'13:34:14'} 0.070543
{'13:34:46'} 0.13177
[snip]
>> t1.TimeStamp = days(t1.TimeStamp); t1.TimeStamp.Format = "hh:mm:ss.SSS";
TimeStamp Head_mm_
____________ ________
13:31:43.000 0
13:31:44.000 1.2
13:31:45.000 1.2
13:31:45.999 0.7
13:31:47.000 0.8
[snip]
>> t2.TimeStamp = duration(t2.TimeStamp); t2.TimeStamp.Format = "hh:mm:ss.SSS"
t2 =
45×2 table
TimeStamp Uy
____________ ___________
13:32:04.000 0.0023132
13:33:09.000 0.068063
13:33:42.000 0.056888
13:34:14.000 0.070543
13:34:46.000 0.13177
[snip]

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More Answers (1)

Walter Roberson
Walter Roberson on 13 Mar 2022
th = datetime(Hdat.TimeStamp);% convert to datetime array
You did not use any options when you readtable(): how can you be sure that TimeStamp was read in as either string array or cell array of character vectors? How do you know that the format was not recognized and it might already have been converted to datetime? Or perhaps the column got misidentified as numeric?
  7 Comments
Peter Perkins
Peter Perkins on 14 Mar 2022
I can't answer that. You need to have at least some idea what is in your data files. datetime assumes that if you give it a partial (time-only) timestamp, you mean "today". In my opinion, your data files are the culprit and are not formatted properly.

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