Claudio,

If you would like to extract specific data from your worksheet based on a specific column of a worksheet, try using Extract Worksheet Data. This feature can be accessed by selecting Analysis => Extract Worksheet Data when the worksheet is active. An explanation on how to use this feature is located in the Origin User's manual (p. 70 for 4.0/4.1 English users and p. 60 for 5.0 English users). If the explanation is still not enough, below are a couple of examples I prepared based on the examples you provided.

1. To extract every n^th row of a worksheet, enter mod(i,n)==0 in the text box provided in Extract Worksheet Data. The value for n is arbitrary. In your case, the value would be 3. If you are unfamiliar with the mod(x,y) function, be sure to take a look at either the Origin 5.0 LabTalk manual (English) on page 355 or the Origin 4.0 User's manual (English) on page 392 for an explanation.


2. To extract specific rows of the worksheet where the cell value of the reference column exceeds a specified value (call it x), enter col(referencecolumnname)>x where referencecolumnname and x are up to you to enter.
   

   Note: You can use the < (less than), <= (less than or equal to) , == (equal to), != (not equal to), >= (greater than or equal to), && (And), and/or | | (Or) operators in addition to the > (greater than) operator in this dialog box.

   
   

Sincerely,
Ryan Toomey