ColdFusion Day 41:

ColdFusion Day 41:

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WORKING WITH COLDFUSION DATA STRUCTURES

* Understanding and Using Lists: More than just strings.

* Understanding and Using Arrays.

* Understanding and Using Structures and Associated Arrays.

So far in the book, you have worked with simple data types: numbers, strings, Boolean values, and the like. ColdFusion, however, supports a collection of more advanced data types common to most programming languages.

In ColdFusion, these more sophisticated data types are lists, arrays, and structures. In all cases, these data types combine collections of simpler data types into a more complex, structured relationship.

For instance, a list is just that, a list of strings, in a predefined order. An array is an ordered collection of data type including numbers, strings, Boolean values, and lists.

Structures are new in ColdFusion 4. They offer the capability to create sets of relationships by mapping one set of values to its counterpart in another set of values.

Applying these data types opens the door to new possibilities in your ColdFusion templates.

UNDERSTANDING AND USING LISTS: MORE THAN JUST STRINGS

You have already had a brief introduction to lists. In Chapter 7, "Controlling the flow of your templates," you encountered lists as the value of the VALUE attribute of the CFCASE tag in a switch-case construct.

A list is simply a string value structured in a special way; it is a series of shorter strings separated by a delimiter. For instance, the following are all lists:

"A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z"

"1;2;3;4;5;6;7;8;9;0"

"ab|c|defg|h|i|jkl|mno|pqrstuvwxy|z"

In all cases, the lists have a delimiter (the three used here are a comma, a semicolon, and a vertical bar or pipe). These delimiters separate list elements that consist of one or more characters other than the delimiter character.

Lists can also contain more than one delimiter character. For instance, the following list can be interpreted in several ways:

"1,2|3,4"

There are three ways to break up this list depending on the selection of the delimiter character:

* A two-element list ("1,2" and "3,4") with a vertical bar as the delimiter.

* A three-element list ("1" and "2|3" and "4") with a comma as the delimiter.

* A four-element list ("1" and "2" and "3" and "4") with both commas and vertical bars as delimiters.

Another aspect of lists is that delimiters can be more than one character long. For instance, in the list "ab,|cd" if both commas and vertical bars are valid delimiter characters, then the list has two elements: "ab" and "cd".

NOTE When working with lists, you can generally assume that the delimiter is a comma unless otherwise specified. In most of the functions and tags that work with lists, a comma is treated as the default delimiter unless others are specified.

ColdFusion provides several functions that you can use to create and manipulate the content of lists. You will take a close look at the following functions in this section:

* ListLen

* ListFirst

* ListLast

* ListRest

* ListAppend

* ListPrepend

* ListChangeDelims

* ListGetAt

* ListInsertAt

* ListSetAt

* ListDeleteAt

* ListFind

* ListFindNoCase

* ListContains

* ListContainsNoCase

ListLen

Because a list consists of a series of elements, when working with lists you need to be able to determine the number of elements in a list. The ListLen function returns the number of elements in a list passed as an argument:

ListLen(List,Delimiters). If no delimiters are specified, the default comma is assumed to be the delimiter.

For instance, the following code:

#ListLen("1,2|3,4","1")#<BR>

#ListLen("1,2|3,4)#<BR>

#ListLen("1,2|3,4",",|")#

</CFOUTPUT>

produces the following output:

Notice the use of the second argument to specify delimiters in the first and last lines of the output. The last line specifies multiple delimiters (the comma and the vertical bar) by simply including them in the string that is the delimiter argument. In the second line of the output, no delimiter is specified, which means that a comma is the delimiter.

ListFirst returns the first element in a list given an argument and an optional delimiter definition: ListFirst(List,Delimiters). As an example, the following code:

#ListFirst("1,2|3,4","1")#<BR>

#ListFirst("1,2|3,4)#<BR>

#ListFirst("1,2|3,4",",|")#

</CFOUTPUT>

produces the following output:

1,2

ListLast As expected, ListLast performs the opposite job of ListFirst: It returns the last element in a list. ListLast takes the form ListLast(List,Delimiters).

ListRest As a corollary to ListFirst, ListRest returns a given list except for the first element. Used together, ListFirst and ListRest return all elements in a list. As would be expected, ListRest takes the form ListRest(List,Delimiters).

Listing 13.1 shows the complementary roles of ListFirst and ListRest.

Listing 13.1: listrest.cfm

<TR>

<TD>DELIMITER</TD>

<TD>FIRST</TD>

</TR>

<TR>

<TD>#ListFirst("1,2|3,4","1")#</TD>

<TD>#ListRest("1,2|3,4","1")#</TD>

</CFOUTPUT>

</TR>

<TR>

<TD>#ListFirst("1,2|3,4","1")#</TD>

<TD>#ListRest("1,2|3,4","1")#</TD>

</CFOUTPUT>

</TR>

<TR>

<TD>#ListFirst("1,2|3,4","1")#</TD>

<TD>#ListRest("1,2|3,4","1")#</TD>

</CFOUTPUT>

</TR>

</TABLE>

This code produces results like those in figure 13.1 which can be viewed online at http://www.accc.net.au/sybex/listrest.cfm

Figure 13.1: Using ListRest

DELIMITER FIRST REST

| 1,2 3,4

, 1 2|3,4

,| 1 2|3,4

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