I am working on expanding this sketch: http://www.openprocessing.org/sketch/11045
Trying to add aging to boids agents using frameCount.
I initialise ArrayList with age inbuilt:
boids = new ArrayList();
for (int i = 0; i < boidNum; i++) {
Agent boid = new Agent(random(width), random(height), 1, round(frameCount + random(300, 400)));
boids.add(boid);
}
Then retrieve it :
Agent(float posX, float posY, int t, int a) {
mass = 5.0;
location = new PVector(posX, posY);
vel = new PVector(random(-5,5), random(-5, 5));
acc = new PVector();
type = t;
wdelta = 0.0;
action = 0;
age = a;
}
I want to use something like this for the living cycle :
if (frameCount != age) {
age = age - 1;
}
if (frameCount == age) {
boids.remove(this);
}
But I'm not sure where in the code I should put it.
Also is this the best way to do it, or am I overcomplicating things?
Update:
I wrote a new method:
void boid(ArrayList boids) {
for (int i = 0; i < boids.size(); i++) {
if (frameCount >= age) {
boids.remove(this);
}
}
}
which is being called from:
void steer(ArrayList boids, ArrayList predators, ArrayList landscape) {
if (type == 1) boid(boids); ...
It sounds like you would want to put that code in the Agent class, after you do the updating and drawing of the Agent- taking a quick look at the code, that's probably the run() function in the Agent class.
But I'm not totally sure why you're comparing each Agent's age with the frameCount. The frameCount variable just tells you how long the sketch has been running. You if statement kills any birds that have the same age as the sketch, which doesn't make any sense.
Instead, you need to have two variables in your Agent class: the age variable that starts at 0 and increments by one each frame, and a maxAge variable that stores the age at which the Agent should be removed.
If you want some friendly advice though, I'd really recommend starting over from scratch with your own code instead of trying to modify an existing one, especially if you aren't really sure how the code works yet. It might seem like you're saving time by using existing code, but if you don't really know how code works yet, you'll definitely save yourself a bunch of headaches by writing it yourself. Up to you though.
Related
I've read somewhere that a variable should be entered into the code if it is reused. But when I write my code for logic transparency, I sometimes create intermediate variables (with names reflecting what they contain) which are used only once.
How incorrect is this concept?
PS:
I want to do it right.
It is important to note that most of the time clarity takes precedence over re-usability or brevity. This is one of the basic principles of clean code. Most modern compilers optimize code anyway so creating new variables need not be a concern at all.
It is perfectly fine to create a new variable if it would add clarity to your code. Make sure to give it a meaningful name. Consider the following function:
public static boolean isLeapYear(final int yyyy) {
if ((yyyy % 4) != 0) {
return false;
}
else if ((yyyy % 400) == 0) {
return true;
}
else if ((yyyy % 100) == 0) {
return false;
}
else {
return true;
}
}
Even though the boolean expressions are used only once, they may confuse the reader of the code. We can rewrite it as follows
public static boolean isLeapYear(int year) {
boolean fourth = year % 4 == 0;
boolean hundredth = year % 100 == 0;
boolean fourHundredth = year % 400 == 0;
return fourth && (!hundredth || fourHundredth);
}
These boolean variables add much more clarity to the code.
This example is from the Clean Code book by Robert C. Martin.
I am taking an introduction to Java programing class and I have an array list where I need to exclude the first element from my for loop that finds an average. The first element in the array list is a weight for the average (which is why it needs to be excluded). I also need to drop the lowest value from the remainder of the array list hence my second for loop. I have tried to create a copy of the list and also tried to create a sub list but I cannot get it to work.
public static double Avgerage(ArrayList<Double> inputValues) {
double avg;
double sum = 0;
double weightValue = inputValues.get(0);
double lowest = inputValues.get(0);
for (int i = 1; i > inputValues.size(); i++) {
if (inputValues.get(i) < lowest) {
lowest = inputValues.get(i);
}
}
for (int i = 0; i < inputValues.size(); i++) {
sum = sum + inputValues.get(i);
}
double average = (sum - lowest) / (inputValues.size() - 1);
avg = average * weightValue;
return avg;
}
To start with good programming practice, you should work with interfaces rather than classes, where possible. The appropriate interface here is List<Double>, and when you create it in your class, you should use
List<Double> nameOfList = new ArrayList<Double>();
What we're doing is creating an object which has the behaviour of a List, with the underlying implementation of an ArrayList (more info here.
With regards to the question, you don't appear to be excluding the first element, as you said you wished to - both for loops iterate through all values in the list. Remember to treat the ArrayList like an array - accessing an element does not modify it, like it might in a Queue.
I have edited your code below to demonstrate this, and have also included some other optimisations and corrected the sign error on line 7:
public static double average(List<Double> inputValues) {
double sum = 0;
//Exclude the first element, as it contains the weight
double lowest = inputValues.get(1);
for (int i = 2; i < inputValues.size(); i++) {
lowest = Math.min(inputValues.get(i), lowest);
}
for (int i = 1; i < inputValues.size(); i++) {
sum += inputValues.get(i);
}
double average = (sum - lowest) / (inputValues.size() - 1);
//Scale by the weight
avg *= inputValues.get(0);
return avg;
}
Note: The convention in java is to use camelCase for method names, I have adjusted accordingly.
Also, I don't know your requirements, but optimally, you should be providing logical parameters. If possible do the following before calling the function:
int weight = inputValues.get(0);
inputValues.remove(0);
//And then you would call like this, and update your method signature to match
average(inputValues, weight);
I don't do this inside the method, as the context implies that we would not be modifying values.
When you have code like this (written in java, but applicable to any similar language):
public static void main(String[] args) {
int total = 0;
for (int i = 0; i < 50; i++)
total += i * doStuff(i % 2); // multiplies i times doStuff(remainder of i / 2)
}
public static int doStuff(int i) {
// Lots of complicated calculations
}
You can see that there's room for improvement. doStuff(i % 2) only returns two different values - one for doStuff(0) on even numbers and one for doStuff(1) on odd numbers. Therefore you're wasting a lot of computation time/power on recalculating those values each time by saying doStuff(i % 2). You can improve like this:
public static void main(String[] args) {
int total = 0;
boolean[] alreadyCalculated = new boolean[2];
int[] results = new int[2];
for (int i = 0; i < 50; i++) {
if (!alreadyCalculated[i % 2]) {
results[i % 2] = doStuff(i % 2);
alreadyCalculated[i % 2] = true;
}
total += i * results[i % 2];
}
}
Now it accesses a stored value instead of recalculating each time. It might seem silly to keep arrays like that, but for cases like looping from, say, i = 0, i < 500 and you're checking i % 32 each time, or something, an array is an elegant approach.
Is there a term for this kind of code optimization? I'd like to read up more on the different forms and the conventions of it but I'm lacking a concise description.
Is there a term for this kind of code optimization?
Yes, there is:
In computing, memoization is an optimization technique used primarily to speed up computer programs by storing the results of expensive function calls and returning the cached result when the same inputs occur again.
https://en.wikipedia.org/wiki/Memoization
Common-subexpression-elimination (CSE) is related to this. This case is a combination of that and hoisting a loop-invariant calculation out of a loop.
I'd agree with CBroe that you could call this specific form of caching memoization, esp the way you're implementing it with the clunky alreadyCalculated array. You can optimize that away since you know which calls will be new values and which will be repeats. Normally you'd implement memoization with a static array inside the called function, for the benefit of all callers. Ideally there's a sentinel value you can use to mark entries which don't have a result computed yet, instead of maintaining a separate array for that. Or for a sparse set of input values, just use a hash (instead of e.g. an array with 2^32 entries).
You can also avoid the if in the main loop.
public class Optim
{
public static int doStuff(int i) { return (i+5) << 1; }
public static void main(String[] args)
{
int total = 0;
int results[] = new int[2];
// more interesting if we pretend the loop count isn't known to be > 1, so avoiding calling doStuff(1) for n=1 is useful.
// otherwise you'd just do int[] results = { doStuff(0), doStuff(1) };
int n = 50;
for (int i = 0 ; i < Math.min(n, 2) ; i++) {
results[i] = doStuff(i);
total += i * results[i];
}
for (int i = 2; i < n; i++) { // runs zero times if n < 2
total += i * results[i % 2];
}
System.out.print(total);
}
}
Of course, in this case we can optimize a lot further. sum(0..n) = n * (n+1) / 2, so we can use that to get a closed-form (non-looping) solution in terms of doStuff(0) (sum of the even terms) and doStuff(1) (sum of the odd terms). So we only need the two doStuff() results once each, avoiding any need to memoize.
I am totally new at this whole programming thing, and I really need help. So basically, I'm trying to make a healthbar that will increase or decrease depending on what button is clicked. I made a healthbar movieclip with 101 frames (I included zero) and put this in the actionscript layer of the movieclip:
var health:Number = 0;
if(health == 0)
{
gotoAndStop("1")
}
if(health == 1)
{
gotoAndStop("2")
}
if(health == 2)
{
gotoAndStop("3")
}
and on and on like so. Basically, on the stage itself, I have a button called fortyfiveup_btn that is commanded to do this:
var health:Number = 0;
fortyfiveup_btn.addEventListener(MouseEvent.CLICK, fortyfiveupClick);
function fortyfiveupClick(event:MouseEvent):void{
health = health+45
}
I quickly realized that both health variables, the one for the button and the one for the healthbar will not interact. How can I make it so if the button is clicked, the health goes to the relevant frame or percentage?
Thanks for any answers, and I appreciate all the help I can get :)
If the answer == yes to my comment you should do this:
You need to give the movieclip an instancename (perhaps lifebar) and from stage you can access the health inside the "lifebar" with lifebar.health.
So you need this inside your stage:
//You can delete the var health:Number = 0;
fortyfiveup_btn.addEventListener(MouseEvent.CLICK, fortyfiveupClick);
function fortyfiveupClick(event:MouseEvent):void{
//You can write this, too: lifebar.health += 45;
lifebar.health = lifebar.health+45;
}
You can even optimize your lifebar script, don't use 101 times the if(health == x) you can use this, too:
gotoAndStop(health + 1);
(I think this is inside an ENTER_FRAME event?)
EDIT:
Some error countermeasures:
//Don't let health decrease below 0
if(health < 0) health = 0;
//And don't above 100
else if(health > 100) health = 100;
gotoAndStop(health + 1);
Use int instead of Number when you don't use decimal numbers and uint when you don't use negative integers (this bugs when the number can drop under 0, so for your health we take int):
health:int = 0;
I brute-forced summing of all primes under 2000000. After that, just for fun I tried to parallel my for, but I was a little bit surprised when I saw that Parallel.For gives me an incorrect sum!
Here's my code : (C#)
static class Problem
{
public static long Solution()
{
long sum = 0;
//Correct result is 142913828922
//Parallel.For(2, 2000000, i =>
// {
// if (IsPrime(i)) sum += i;
// });
for (int i = 2; i < 2000000; i++)
{
if (IsPrime(i)) sum += i;
}
return sum;
}
private static bool IsPrime(int value)
{
for (int i = 2; i <= (int)Math.Sqrt(value); i++)
{
if (value % i == 0) return false;
}
return true;
}
}
I know that brute-force is pretty bad solution here but that is not a question about that. I think I've made some very stupid mistake, but I just can't locate it. So, for is calculating correctly, but Parallel.For is not.
You are accessing the variable sum from multiple threads without locking it, so it is possible that the read / write operations become overlapped.
Adding a lock will correct the result (but you will be effectively serializing the computation, losing the benefit you were aiming for).
You should instead calculate a subtotal on each thread and add the sub-totals at the end. See the article How to: Write a Parallel.For Loop That Has Thread-Local Variables on MSDN for more details.
long total = 0;
// Use type parameter to make subtotal a long, not an int
Parallel.For<long>(0, nums.Length, () => 0, (j, loop, subtotal) =>
{
subtotal += nums[j];
return subtotal;
},
(x) => Interlocked.Add(ref total, x)
);
Many thanks to all of you for your quick answers
i changed
sum += i;
to
Interlocked.Add(ref sum,i);
and now it works great.