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Topic: append array multi dimension (Read 394 times) |
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st33d
 
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append array multi dimension
« on: Jul 29th, 2004, 2:34am » |
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Code:
int []x=new int [1];
void setup(){
x[0]=1;
}
void draw(){
newLength(x[x.length-1]);
println(x[0]);
println(x[1]);
println(x.length);
}
void newLength(int newx) {
int[] tempx = new int[x.length + 1];
System.arraycopy(x, 0, tempx, 0, x.length);
tempx[x.length] = newx;
x = tempx;
}
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This code is based on a previous post I looked up to find out how to append an array. It has served me well but I must prevail upon the wisdom of the forum in another matter. How do I append a multi-dimensional array? Lets say our array is x[][], what is the correct syntax for extending the length of either of the dimensions?
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I could murder a pint.
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narain
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Re: append array multi dimension
« Reply #1 on: Jul 29th, 2004, 6:06am » |
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That's tough, actually, because of the way multi-dimensional array work...
When you say int x[m][n], what Java does is actually to create m independent arrays of n ints each, and then make an array of those.
So to extend the array in the first dimension, you can just treat x as a simple array containing int[]s, like this (untested):
Code:void extend1 (int[] newx) {
// newx is what to put in the new locations
int[] tempx = new int[x.length+1][];
System.arraycopy(x, 0, tempx, 0, x.length);
tempx[x.length] = newx;
x = tempx;
} |
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Extending in the second dimension is harder, since x has m arrays of n elements, so to increase n you'll have to extend each one of the m arrays.
(also untested):
Code:void extend2 () {
for (int i = 0; i < x.length; x++) {
int[] xi = x[i];
int[] tempxi = new int[xi.length + 1];
System.arraycopy(xi, 0, tempxi, 0, xi.length);
x[i] = tempxi;
}
}
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This one leaves the new locations unset for clarity. (If you want you can pass another int[] containing what to set in each location).
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st33d
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Re: append array multi dimension
« Reply #2 on: Jul 29th, 2004, 10:21pm » |
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Thanks a bundle. This knowledge comes in especially handy at the conceptual stage.
Code is tested. Try for yourself.
Code:
int [][] x=new int [1][1];
void setup(){
x[0][0]=1;
}
void draw(){
println(x[0][0]);
println(x[0][0]);
extend1(x[x.length-1]);
println(x[1][0]);
extend2();
println(x[1][1]);
println(x.length);
}
void extend1 (int[] newx) {
// newx is what to put in the new locations
int[][] tempx = new int[x.length+1][];
System.arraycopy(x, 0, tempx, 0, x.length);
tempx[x.length] = newx;
x = tempx;
}
void extend2 () {
for (int i = 0; i < x.length; i++) {
int[] xi = x[i];
int[] tempxi = new int[xi.length + 1];
System.arraycopy(xi, 0, tempxi, 0, xi.length);
x[i] = tempxi;
}
}
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I could murder a pint.
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narain
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Re: append array multi dimension
« Reply #3 on: Jul 30th, 2004, 3:42pm » |
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Good for you  Glad to help.
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