Previous Interpolation based on a condition

I have a an array with 2 columns, one is datetime and the next one is values say, rate, I want to use previous interpolation on rate. My condition to do previous interpolation is, when the time is 20 seconds apart and the rate is less than 20, and if rate is greater than 20, I put NaN.

Can you help here?

[Bob Thompson]

I'm a little confused what you mean by 'previous interpolation.' How does this differ from regular interpolation?

Also, is your condition literally this?

dt == 20 & rate < 20 & rate > 20

[Sam17]

i am talking about https://www.mathworks.com/help/matlab/ref/interp1.html where the methos is previous. Yes, that's correct, the condition is that

[Bob Thompson]

So, are you looking for an if statement which contains the interpolation?

if dt == 20 & rate < 20 & rate > 20
    ir = interp1(time,rate,r);
end

Also, you cannot actually meet all of those conditions at once. You're asking to identify a rate value which is both greater than 20, and less than 20 at the same time. Are you sure that there isn't supposed to be an or statement in the conditions? Look for rate values which are less than or greater than 20?

[Sam17]

yes. You can keep that in a different statement. else if rate>20, put all values as Nan

[Bob Thompson]

Ah, I see how it should read now. Yes, you can add that elseif condition to your if statement.

if dt == 20 & rate < 20
    ir = interp1....
elseif rate > 20
    ir = nan;
end

What are you going to do though if rate is exactly 20? You may just want to ignore it, just making sure you have considered the possibility.