Error using interp1

Hi all,

I'm trying to interpolate my data set using interp1.

My data set looks something like:

tympanic.nw1.Time =

'10:04:48'

'10:04:49'

'10:04:50'

'10:04:51'

'10:04:52'

'10:04:53'

tympanic.nw1.Temperature =

35.3000000000000

35.3000000000000

35.4000000000000

35.4000000000000

35.4000000000000

35.3000000000000

35.3000000000000

I used the following code:

% Tympanic Temp
t1 = tympanic.nw1.Time(1,1); t2 = tympanic.nw1.Time(end,1); t = t1:seconds(1):t2; t = t.';
tympanic.nw1.Temperature = interp1(tympanic.nw1.Time, tympanic.nw1.Temperature, t); 
tympanic.nw1.Time = t; 

Matlab gives the following error: Error using griddedInterpolant. Sample points must be unique and sorted in ascending order. Can someone explain me how to solve this problem? I already tried using the function unique, but that didn't solve my problem.

[Rik]

What data type is your time array?

Answer 1

[Star Strider]

Veerle Kohlen —

You likely need to put your data into a timetable array, then use the retime function. That would likely be the easiest way to do it.

Example —

tympanic.nw1.Time  =  ['10:04:48'
                       '10:04:49'
                       '10:04:50'
                       '10:04:51'
                       '10:04:52'
                       '10:04:53'];

tympanic.nw1.Temperature = [35.3000000000000
                            35.3000000000000
                            35.4000000000000
                            35.4000000000000
                            35.4000000000000
                            35.3000000000000];

T1 = table(tympanic.nw1.Time, tympanic.nw1.Temperature);
T1.Var1 = datetime(T1.Var1, 'InputFormat','HH:mm:ss', 'Format','HH:mm:ss');
TT1 = table2timetable(T1);
TT1rt = retime(TT1, 'secondly','TimeStep',1);

EDIT — (7 Dec 2020 at 16:36)

Added the example.

[Veerle Kohlen]

Thank you!

[Star Strider]

As always, my pleasure!