Removing rows from a column depending on another column

Hello,

I need a little bit of help with this problem. I will explain it the best I can then give a basic example below. Basically I have two column vectors. I am trying to split one of them up depending on the other. Basically I have:

 Cp=[0;0.2;0.4;0.6;0.8;1;1.2;1.4];

 Cf=[0;1;2;3;4;5;6;7;8];

I am trying to split up Cf depending on when Cp hits 1. So essentially, when Cp<=1 I am trying to obtain a column for Cf with only those values. So the resultant Cf would be:

 Cf_new=[0;1;2;3;4;5]

So the only values obtained for Cf are when the corresponding row of Cp is less than or equal to 1. I hope this makes sense. Thank you

Answer 1

[Image Analyst]

Regarding your new question about extracting values of Cf only up to and including the index of the peak in Cp:

Cp=[0.2 0.4 0.8 0.99 0.8 0.4 0.2]
Cf=[0;1;2;3;4;5;6;7;8]

peakIndex = find(diff(Cp) < 0, 1, 'first')
Cf_new = Cf(1 : peakIndex)

In the command window:

Cp =  0.2  0.4  0.8  0.99  0.8  0.4   0.2
Cf =
     0
     1
     2
     3
     4
     5
     6
     7
     8
peakIndex =
     4
Cf_new =
     0
     1
     2
     3

Answer 2

[the cyclist]

Cf_new = Cf(Cp<=1);

[Christopher]

I am sorry I made a mistake. My column for Cp never goes above 1 it peaks very close to 1. So it is something like this:

 Cp=[0.2 0.4 0.8 0.99 0.8 0.4 0.2];

So I am trying to obtain Cf for when Cp peaks at 0.99 and below. I apologize for the mistake.

[Azzi Abdelmalek]

Adapt your code to 0.99 instead of 1

[Christopher]

Yes, but the problem is all the values are less than 0.99, so it returns the entire original Cf column. Some how I need to obtain the number of rows from the beginning of Cf until it hits the peak.

[Image Analyst]

That's a different question than you first asked. How are you defining "peak"? There is a findpeaks() function in the Signal Processing Toolbox. Or else you could just call diff(Cp) and look for the first negative value - it just depends on how you want to define a "Peak."

Answer 3

[Andrei Bobrov]

out = Cf(1:find(Cp>=.99,1,'first'));