Tersus: Re: first n numbers of elements in a list

Re: first n numbers of elements in a listDate: Jan 14, 2010Basically, you need to combine Collections/Range (which creates a running index from 1 to N) with Collections/Get Numbered Item (which returns an element from a list by index).One would expect the model to look like the following:

However, the model in the screenshot above will not work, due to the fact that an element (Get Numbered Item), with a repetitive trigger (<List>), cannot be repetitive itself.To overcome this limitation, you will need to implement the following:

Notes:

By using a used-defined container data structure, containing all items (List), we can now pass the items as a non repetitve element, into a repetitive, user-defined container model (Get Numbered Item from List), which encapsulates Get Numbered Item (which is not be repetitive). The end result being that Get Numbered Item from List is executed multiple times, each time causing Get Numbered Item to be executed on the same list of items, with a different index each time.

The use of the Data Types/Anything data type for storing the items, allows this process to be a generic reusable process which you can use with lists of any type. You need to make sure that the relevent slots (triggers/exits), through which the items pass, are also defined as type Anything - do so by dropping the type from the palette onto Get First N Items/Items, Get Numbered Item/<List>, <Get Numbered Item/<Item>, Ge Numbered Item from List/Item, and Get First N Items/First N Items.

The above implementation assummes that N is a positive integer which is not greater than the actual number of items provided. If that is not the case, you will need to add modeling which compares N (using the various Math templates) against the number of items passed (use Collections/Count), and decide what to do if N is invalid, such as display a message, or use the number returned by Count instead of N.

Regards,DavidSee Also:

To use the full functionality of this web site, JavaScript needs to be turned on.

For best results, use the Firefox browser..

Loading ...