You can add an element to an array by assigning the element a value or by using a ColdFusion function.

Adding an array element by assignment

You can add elements to an array by defining the value of an array element, as shown in the following cfset tag:

<cfset myarray[5]="Test Message">

If an element does not exist at the specified index, ColdFusion creates it. If an element already exists at the specified index, ColdFusion replaces it with the new value. To prevent existing data from being overwritten, use the ArrayInsertAt function, as described in the next section.

If elements with lower-number indexes do not exist, they remain undefined. You must assign values to undefined array elements before you can use them. For example, the following code creates an array and an element at index 4. It outputs the contents of element 4, but generates an error when it tries to output the (nonexistent) element 3.

<cfset myarray=ArrayNew(1)>
<cfset myarray[4]=4>
<cfoutput>
    myarray4: #myarray[4]#<br>
    myarray3: #myarray[3]#<br>
</cfoutput>

Adding an array element with a function

You can use the following array functions to add data to an array:

Because ColdFusion arrays are dynamic, if you add or delete an element from the array, any higher-numbered index values all change. For example, the following code creates a two element array and displays the array contents. It then uses ArrayPrepend to insert a new element at the beginning of the array and displays the result. The data that was originally in indexes 1 and 2 is now in indexes 2 and 3.

<!--- Create an array with three elements. --->
<cfset myarray=ArrayNew(1)>
<cfset myarray[1]="Original First Element">
<cfset myarray[2]="Original Second Element">
<!--- Use cfdump to display the array structure --->
<cfdump var=#myarray#>
<br>
<!--- Add a new element at the beginning of the array. --->
<cfscript>
    ArrayPrepend(myarray, "New First Element");
</cfscript>
<!--- Use cfdump to display the new array structure. --->
<cfdump var=#myarray#>

For more information about these array functions, see the CFML Reference.

Deleting elements from an array

Use the ArrayDeleteAt function to delete data from the array at a particular index, instead of setting the data value to zero or an empty string. If you remove data from an array, the array resizes dynamically, as the following example shows:

<!--- Create an array with three elements --->
<cfset firstname=ArrayNew(1)>
<cfset firstname[1]="Robert">
    <cfset firstname[2]="Wanda">
    <cfset firstname[3]="Jane">
<!--- Delete the second element from the array --->
<cfset temp=ArrayDeleteAt(firstname, 2)>
<!--- Display the array length (2) and its two entries,
    which are now "Robert" and "Jane" --->
<cfoutput>
    The array now has #ArrayLen(firstname)# indexes<br>
    The first entry is #firstname[1]#<br>
        The second entry is #firstname[2]#<br>
    </cfoutput>

The ArrayDeleteAt function removed the original second element and resized the array so that it has two entries, with the second element now being the original third element.

Copying arrays

You can copy arrays of simple variables (numbers, strings, Boolean values, and date-time values) by assigning the original array to a new variable name. You do not have to use ArrayNew to create the new array first. When you assign the existing array to a new variable, ColdFusion creates a new array and copies the old array's contents to the new array. The following example creates and populates a two-element array. It then copies the original array, changes one element of the copied array and dumps both arrays. As you can see, the original array is unchanged and the copy has a new second element.

<cfset myArray=ArrayNew(1)>
<cfset myArray[1]="First Array Element">
<cfset myArray[2]="Second Array Element">
<cfset newArray=myArray>
<cfset newArray[2]="New Array Element 2">
<cfdump var=#myArray#><br>
<cfdump var=#newArray#>

If your array contains complex variables (structures, query objects, or external objects such as COM objects) assigning the original array to a new variable does not make a complete copy of the original array. The array structure is copied; however, the new array does not get its own copy of the complex data, only references to it. To demonstrate this behavior, run the following code:

Create an array that contains a structure.<br>
<cfset myStruct=StructNew()>
<cfset myStruct.key1="Structure key 1">
<cfset myStruct.key2="Structure key 2">
<cfset myArray=ArrayNew(1)>
<cfset myArray[1]=myStruct>
<cfset myArray[2]="Second array element">
<cfdump var=#myArray#><br>
<br>
Copy the array and dump it.<br>
<cfset myNewArray=myArray>
<cfdump var=#myNewArray#><br>
<br>
Change the values in the new array.<br>
<cfset myNewArray[1].key1="New first array element">
<cfset myNewArray[2]="New second array element">
<br>
Contents of the original array after the changes:<br>
<cfdump var=#myArray#><br>
Contents of the new array after the changes:<br>
<cfdump var=#myNewArray#>

The change to the new array also changes the contents of the structure in the original array.

To make a complete copy of an array that contains complex variables, use the Duplicate function.