Arrays (javascript) - Revision history

161.253.9.181 at 00:28, 15 April 2005

2005-04-15T00:28:52Z

161.253.9.181: /* concat */

2005-04-14T23:32:28Z

concat

161.253.9.181 at 23:31, 14 April 2005

2005-04-14T23:31:26Z

New page

=Some Perl analogues=

Perl JS
@a = (1,2,3); a = new Array(1,2,3);
@a = (@b,@c,'d'); a = b.concat(c,'d');
@a = ('x',@b,'y',@c); a = new Array('x').concat(b,'y',c);
push(@a,1,2,3) a.push(1,2,3)
pop(@a) a.pop() // returns undefined if empty
unshift(@a,4,5,6) a.unshift(4,5,6) // array is now led by 4,5,6
shift(@a) a.shift()
@a[0..4] a.slice(0,4+1)
reverse(@a) a.reverse()
@a = sort(@a); a.sort();
@b = sort(@a); b = a.slice(0); b.sort();
@a = sort {cf($a,$b)} @a; a.sort(cf); // cf has typical compare semantics
scalar(@a) a.length // not a method, a property

=Constructing=

a = new Array("one","two","three");

=concat=

Combine multiple arrays and non-arrays into a single flat array.

a = new Array('B','C','D');
b = new Array('G','H','I');

c = new Array('A').concat(a,'E','F',b,'J','K');
// c contains 'A','B','C','D','E','F','G','H','I','J','K'

=join=

Make a string containing all elements in order.

a.join(separator);

=slice=

Copy out a segment of the array.

a.slice(beginIndex,postIndex);
a.slice(beginIndex,lastIndex+1);

If beginIndex is negative, it is treated as a.length + beginIndex. If postIndex is negative, it is treated as a.length + postIndex. If postIndex is before beginIndex, the result is an empty array.

Omitting postIndex copies to the end of the array. Specifying postIndex >= a.length has the same effect.

a.slice(0) returns a full copy of a.

=splice=

Delete and replace some elements of an array.

a.splice(beginIndex,count,replacement,...);
a = new Array(0,1,2,3,4,5);
a.splice(1,3,"yow","za");
// a is now 0,"yow","za",4,5

Number of replacement elements does not need to match number removed. If number removed exceeds number remaining, all remaining are removed. Arrays in replacement are ''not'' flattened.

=reverse=

Sx.

ar = a.reverse();

← Older revision		Revision as of 00:28, 15 April 2005
Line 65:		Line 65:

	ar = a.reverse();		ar = a.reverse();
		+
		+	=arrayCopy=
		+
		+	In JavaScript, there is no in-place arrayCopy method like there is in Java. If the operation you want to do absolutely must be in-place, this function will do the element-by-element work for you:
		+
		+	function arrayCopy(src,srcIndex,dest,destIndex,length)
		+	{
		+	while(length--)
		+	dest[destIndex+length] = src[srcIndex+length];
		+	}
		+
		+	On the other hand, if creating a new array with the same result as ''dest'' would have received in arrayCopy() will work, take a look at arrayReplace() here, which is implemented in terms of listMultiply() and arrayPadTo():
		+
		+	function listMultiply(v,count)
		+	{
		+	// Use a clever doubling mechanism.
		+	r = (count & 1) ? new Array(v) : new Array();
		+	v = new Array(v);
		+	count >>= 1;
		+
		+	while(count > 0) {
		+	// Double the cache.
		+	v = v.concat(v);
		+	// Maybe add it to the result.
		+	if(count & 1) {
		+	r = r.concat(v);
		+	}
		+	// Continue.
		+	count >>= 1;
		+	}
		+
		+	return r;
		+	}
		+
		+	function arrayPadTo(a,length)
		+	{
		+	if(a.length < length)
		+	a = a.concat(listMultiply(void 0,length-a.length));
		+	return a;
		+	}
		+
		+	function arrayReplace(src,srcIndex,dest,destIndex,length)
		+	{
		+	// Same semantics as arrayCopy from Java.
		+	// But it won't work in place.
		+	return dest.slice(0,destIndex).concat(
		+	arrayPadTo(src.slice(srcIndex,length),length),
		+	dest.slice(destIndex+length) );
		+	}

@@ Line 26: / Line 26: @@
   a = new Array('B','C','D');
   b = new Array('G','H','I');
-−
   c = new Array('A').concat(a,'E','F',b,'J','K');
   // c contains 'A','B','C','D','E','F','G','H','I','J','K'