Looping string array into parsed timestamp

I have the following data that I would like to parse into hours:minutes:secs to plot against other data.

Here is my code that is causing issues with the indexing.

TS = ["085423","085428","085431","085502"];
TS = TS';
for i = 1:length(TS)
    timestr = TS(i);
end
hours = timestr(1:2);
minutes = timestr(3:4);
secs = timestr(5:6);

formatted_time_str = [hours, ':', minutes, ':', secs];

Any insight is appreciated. Thank you.

Answer 1

[Stephen23]

"... that is causing issues with the indexing."

Because you are mixing up indexing into string arrays with the characters contained within them. Not the same things at all: indexing into a string array indexes into the string array, not into the characters it contains (as you incorrectly assumed).

TS = ["085423","085428","085431","085502"]

TS = 1x4 string array
    "085423"    "085428"    "085431"    "085502"

Method one: returns a string array:

FS = extractBefore(TS(:),3)+":"+extractBetween(TS(:),3,4)+":"+extractAfter(TS(:),4)

FS = 4x1 string array
    "08:54:23"
    "08:54:28"
    "08:54:31"
    "08:55:02"

Method two: returns a char matrix:

FS = repmat(':',numel(TS),8);
FS(:,[1:2,4:5,7:8]) = char(TS(:))

FS = 4x8 char array
    '08:54:23'
    '08:54:28'
    '08:54:31'
    '08:55:02'

[James]

Can this be put into the loop, as I have more than 1000 files that need to be processed?

I've only showed 4 here for simplicty.

Thank you

[Stephen23]

"Can this be put into the loop, as I have more than 1000 files that need to be processed? I've only showed 4 here for simplicty."

Sure, put it in a loop if you so desire.

Note that that code I gave you will process any number of text elements, not just four of them.

[James]

In trying to plot the FS data (timestamp) against numerical data I get an error message:

scatter(FS,(1:5).^2)

Error using scatter
Input arguments must be numeric, datetime, duration or categorical.

I've tried to convert the FS data to numeric using:

FS = cellstr(FS);

FS = str2num(FS);

But I get the following error:

Error using str2num
Input must be a character vector or string scalar.

Thanks

[Stephen23]

"In trying to plot the FS data (timestamp) against numerical data I get an error message:"

If you are trying to plot with this data, then you are likely much better of using DURATION objects rather than fiddling around with text or numerics:

TS = ["085423";"085428";"085431";"085502"];
H = str2double(extractBefore(TS(:),3));
M = str2double(extractBetween(TS(:),3,4));
S = str2double(extractAfter(TS(:),4));
D = duration(H,M,S)

D = 4x1 duration array
   08:54:23
   08:54:28
   08:54:31
   08:55:02

Y = rand(size(D));
scatter(D,Y)

[James]

Thank you!