Find the max amplitude of Frequency from text file

I have a text file like this

0.000000,-1.721511E-5,-2.869001E-5
3.906250E-5,-1.859251E-5,-3.247638E-5
7.812500E-5,-2.083079E-5,-2.504133E-5
0.000117,-1.996991E-5,-2.779505E-5
0.000156,-1.866138E-5,-3.044551E-5
0.000195,-2.241480E-5,-2.982592E-5
0.000234,-2.027983E-5,-2.579860E-5
0.000273,-1.786938E-5,-2.497249E-5
0.000312,-1.910904E-5,-2.741642E-5
.......
0.000352,-1.749059E-5,-2.748526E-5
0.000391,-2.141618E-5,-2.855233E-5
0.000430,-2.062418E-5,-2.751968E-5
0.000469,-1.817929E-5,-2.696894E-5
0.000508,-1.511457E-5,-3.030782E-5
0.000547,-1.931565E-5,-2.597071E-5
0.000586,-1.855808E-5,-3.158142E-5
0.000625,-2.072748E-5,-3.054877E-5
0.000664,-2.072748E-5,-3.171910E-5
0.000703,-1.917791E-5,-3.047993E-5
0.000742,-2.289689E-5,-2.486922E-5
0.000781,-2.165723E-5,-2.941286E-5
0.000820,-2.076192E-5,-3.068646E-5
0.000859,-1.776607E-5,-2.583303E-5
0.000898,-1.728398E-5,-2.748526E-5

First colum is value of time, Second and 3rd colum is value of frequency at point 1 and 2. I need to get the max and the second max value of amplitude of frequency at point 1, because maybe there are some bad value of amplitude of frequency at point 1. Then, I need to export the value of the range in the black box. How can I do it.

Answer 1

[Abhiram Bhanuprakash]

Hi Vu,

In your case, since you have only text data (without character strings), I think you can save your data into a CSV file, and use 'csvread' to import the data into the MATLAB workspace. Documentation for 'csvread' is here

After you get the data into MATLAB, you can use it for further processing. For example, in your case, you can use something like:

a = csvread('data.csv'); %where data.csv file contains the data which you have pasted here
maxval = max(a(:,2)); %maximum of second column

To import data from a general text file, you can use 'textscan'. Documentation here

Hope this helps,

Cheers!

Abhiram.

[vu ngothanh]

Hi Abhiram,

In Matlab, we can use

y=load('velo_035.txt');

Because, the time in my text file is very short, and my file is content the FREQUENCY, so, 1 cycle have alot of value. So, in your way, the next maxvalue maybe smaller but it still in the same cycle. I need the second max value in different cycle.

Thank for your time

[Walter Roberson]

You will need to define what a cycle looks like then.

[vu ngothanh]

It is hard to say by word, I'm not good in English. when you zooming the grahp. you will see. Sorry about my bad.

[Abhiram Bhanuprakash]

@vu: Sorry but I am not able to understand you. As Walter has asked, can you please define what you mean by a cycle?

[vu ngothanh]

http://en.wikipedia.org/wiki/Frequency cycles in my mean is T which T=1/f so hard to explain. sorry about that

Answer 2

[Walter Roberson]

fid = fopen('YourFile.txt');
C = textscan(fid, '%f,%f,%f', 'CollectOutput', 1);
close(fid);

point1 = C{1}(:,2);

[up1, upa] = unique(point1);
maxp1 = up1(end);
maxp1pos = upa(end);
max2p1 = up1(end-1);
max2p1pos = upa(end-1);

Note that you have not clearly defined "second maximum" if what you might have is a peak over several values rather than a single bad point.

[vu ngothanh]

Hi Walter,

My file content the FREQUENCY of one element in a short time. In my file, to show 1 cycle, it need alot of value. I think, if we remove the biggest value to get the second biggest value like that, it can be done, but, that second value like that may be in the same cycle. I need the second max value but in the different cycle. Do you mean what I say. Sorry, my english is not too good.

Thank you for your time.