cfGetEveryNthValue ( pList ; pStart ; pIncrement ; pInputSeparator ; pOutputSeparator )

Extract every Nth item from a list; allow starting value and list separators to be specified

Average rating: 4.2 (43 votes) Log in to vote

Kevin Frank - Show more from this author
Kevin Frank & Associates
https://filemakerhacks.com

Sample input:

cfGetEveryNthValue ( "A~B~C~D~E~F" ; 2 ; 3 ; "~" ; "$" )

Sample output:

B$E

Function definition: (Copy & paste into FileMaker's Edit Custom Function window)

/* 
Purpose:   Extract every Nth item from a list; allow starting value and list separators to be specified

Author:   Kevin Frank & Associates  (www.kevinfrank.com) 

Usage:    cfGetEveryNthValue ( pList ; pStart ; pIncrement ; pInputSeparator ; pOutputSeparator )

Example: 
cfGetEveryNthValue ( "A~B~C~D~E~F" ; 2 ; 3 ; "~" ; "$" ) = "B$E"

Note:   if you leave pInputSeparator and/or pOutputSeparator blank, ¶ will be used, e.g., 
cfGetEveryNthValue ( "A¶B¶C¶D¶E¶F" ; 1 ; 2 ; "" ; "" ) = "A¶C¶E"
*/

Let ( [ 
theInputSeparator = If ( IsEmpty ( pInputSeparator ) ; ¶ ; pInputSeparator ) ; 
theOutputSeparator = If ( IsEmpty ( pOutputSeparator ) ; ¶ ; pOutputSeparator ) ; 
theList = If ( theInputSeparator <> ¶ ; Substitute ( pList ; theInputSeparator ; ¶ ) ; pList ) 
] ; 

GetValue ( theList ; pStart ) & 

If ( 
   ValueCount ( theList ) >= ( pStart + pIncrement ) ; 
   theOutputSeparator & cfGetEveryNthValue ( pList ; pStart + pIncrement ; pIncrement ; pInputSeparator ; pOutputSeparator ) 
)

)   //   end let

Recently I needed to reduce a list to "every other" item in that list, i.e., the 1st item, the 3rd item, the 5th item, etc.

It occurred to me that in the future I might need, say, every third item rather than every other item, and that I might want to begin with something other than the first item on the list. It also occurred to me that I might want to specify a list separator other than a hard return, for either the input, the output, or both.

That's how this CF came to be.

Comments

		David Nahodyl, Atlanta, GA May 9, 2015
This worked perfectly for what I needed to do. Giant list of 2800 points to graph, more than necessary and more than WebDirect could handle in a graph. I was about to write my own function and came across this by chance for another project. Thanks for posting this!

Note: these functions are not guaranteed or supported by BrianDunning.com. Please contact the individual developer with any questions or problems.

cfGetEveryNthValue ( pList ; pStart ; pIncrement ; pInputSeparator ; pOutputSeparator )

Comments

Support this website.

Support this website.