How do I cut down the size of an array of data?

I have a few arrays, with one column each, of different sizes (200127, 200126, 200120, etc.) In order to preform the calculations I want to do, I need them to all be the same length. Is there a way to cut them all down to the smallest array I have?

[Bennett Torrance]

I figured out a (possibly inefficient) way of doing it by using the line:

Flow([200121 200122 200123 200124 200125 200126 200127], :) = [];

where flow is the name of the array and I'm using the line to take off the last 7 data points in order to get it down to my smallest array.

There's got to be a better way to do this tho...

Answer 1

[dpb]

It'd be easier if there weren't different variables, but since they're inconsistent in length that makes it a little more of a pain unless you were to initially use a cell array where each cell column contained one of these arrays.

But, the syntax you're looking for to do the size reduction is

[mn,imn]=min(length(A),length(B),...,length(Z));  % minimum length of all your arrays and which one
A(N+1:end)=[];
B(N+1:end)=[];
C(N+1:end)=[];
 ...   % you get the picture, excepting, of course for whichever variable it is that corresponds to variable imn

Alternatively, you can save instead of cull...

A=A(1:N);
B=B(1:N);
C=C(1:N);
...

this way you don't need to worry about which doesn't have >N elements.

Of course, going on into the problem, you'll undoubtedly want to end up with

Data=[A(1:N) B(1:N) C(1:N) ... Z(1:N)];

so you can now programmatically address all by simply using subscripting expressions instead of having superfluous variables to deal with.

How were these arrays created in the first place? Quite possibly you could have solved all the issues while reading them or some other way before got into this fix.

[Bennett Torrance]

Its data that I didn't collect from a hydraulic pump that I'm tasked to calculate the efficiency from. I guess the data acquisition of the different probes (shaft speed, flow, pressure, torque, etc) stopped at different times so the sizes of the arrays are off by a tiny bit.

Thanks for the help!

[dpb]

Yeah, but how did you read those into Matlab? Why not fix up the problem at that point instead of making all those arrays?

Actually, unless they're just huge or there are 10's of thousands of 'em, simply looping thru, reading each into a variable and finding how long they are and getting the minimum is trivial.

Once you've done that, go back and read "in anger" into a variable trimming to the common length and storing into the alternate accumulating array. Gets rid of all the superfluous variables nearly painlessly that way.

[Bennett Torrance]

They are .dat files converted into matlab files with thousands of data points. And I just do analysis I don't collect data so not really my say...

[dpb]

I'm talking about how to do the analysis more effectively than writing a zillion individual variables that leaves you in the quandary you're currently in, given the data as you've been given it.