Beefy Boxes and Bandwidth Generously Provided by pair Networks
Just another Perl shrine

Comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

OK, so then my question is, how do you know when you have valid data, instead of just noise? That is, you might have input with a fairly small variation, where the peaks aren't all that much higher than the valleys. Would you be able to distinguish whether you had any good data among the noise? If so, how? What makes your values good or bad?

There needs to be some means of determining what your good input is. It could be the absolute magnitude of your values (a threshold value, say 500 in this case). However, you said that this wouldn't work - the noise levels, and presumable the levels of the good data, would be variable, so 500 might be within the noise range sometimes.

So another means might be if you knew how many good points you're supposed to have. In that case, simply order the points by value, and grab the top X% of them as "good", and ignore the rest. However, this requires that you know how many good points you're supposed to have.

If this is something that is somewhat periodic, you could use an FFT to get a set of frequencies out of the data; then apply the Kronecker delta function ($kron= $val>$threshold? $val: 0). That basically means, get rid of the frequencies that are not strongly represented in the data. Then do the inverse FFT to get your data back, minus the noise caused by unwanted frequencies. This would only work if you knew your data should be hovering around some definite set of frequencies, and not be all over the spectrum. Check out MathWorld for much more information on FFT, the Kroneker delta, and all that good stuff.

Finally, you can only do so much with bad data. You may need to take a look at the data source itself, if possible, and modify it to try to eliminate the noise at the very beginning.

In reply to Re: How do I find peaks in noisy data? by spiritway
in thread How do I find peaks in noisy data? by tamaguchi

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and all is quiet...

    How do I use this? | Other CB clients
    Other Users?
    Others surveying the Monastery: (7)
    As of 2017-12-15 12:22 GMT
    Find Nodes?
      Voting Booth?
      What programming language do you hate the most?

      Results (431 votes). Check out past polls.