How to create simple array in Ruby? - ruby

What is the shortest way to create this array in Ruby:
[10, 20, 30, 40, 50, 60, 70, 80, 90, 100]
Thanks for any help!


What about Range#step:
(10..100).step(10).to_a
#=> [10, 20, 30, 40, 50, 60, 70, 80, 90, 100]
Or Numeric#step:
10.step(100, 10).to_a
#=> [10, 20, 30, 40, 50, 60, 70, 80, 90, 100]


You can use Range and call Enumerable#map method on it, like this:
(1..10).map{|i| i * 10}
# => [10, 20, 30, 40, 50, 60, 70, 80, 90, 100]
Or, as suggested by #JörgWMittag, with Object#method method that returns Method instance which is converted to proc by & notation:
(1..10).map(&10.method(:*))
# => [10, 20, 30, 40, 50, 60, 70, 80, 90, 100]


This builds an array directly from the constructor.
Array.new(10){|i| (i + 1) * 10}
# => [10, 20, 30, 40, 50, 60, 70, 80, 90, 100]

Related

doubly array from a stream of integers

how to convert Flux<List> into Flux<int[][]>.
I have a Flux<List> -> {1,2,3,.....100} I want to group them by 30 numbers -> [[1,2,3,.....30], [31,32....60],[61.....100]]
I have tried the below approach but was not successful. elements are getting grouped in batches of 5 [ [1,2,3,4,5], [6,7,8,9,10],.....]
Flux<int[][]> groupedData = fluxData.map(x -> {
int outerArraySize = (int) Math.ceil(x.size() / 30) +1;
System.out.println(outerArraySize);
int[][] boxedData = new int[30][outerArraySize];
AtomicInteger innerArray = new AtomicInteger(0);
AtomicInteger outerArray = new AtomicInteger(0);
x.forEach(ids -> {
boxedData[innerArray.get()][outerArray.get()] = ids;
innerArray.getAndIncrement();
if (innerArray.get() == 30) {
innerArray.set(0);
outerArray.getAndIncrement();
}
});

Flux has a useful operator called 'buffer', we can use it to batch the List of Integers.
I have created my 'fluxData' like this, just so I can test my code:
List<Integer> list1 = IntStream.rangeClosed(1, 100).boxed().collect(Collectors.toList());
List<Integer> list2 = IntStream.rangeClosed(1, 40).boxed().collect(Collectors.toList());
List<Integer> list3 = IntStream.rangeClosed(1, 70).boxed().collect(Collectors.toList());
Flux<List<Integer>> fluxData = Flux.just(list1, list2, list3);
Now, we can do the following:
fluxData.map(integersList -> {
List<List<Integer>> batchesList = Flux.fromStream(integersList.stream())
.buffer(30) // This the magic.
.collectList()
.block();
// List<List<Integer>> --> int[][]
int[][] batchesArray = new int[batchesList.size()][];
for(int i = 0;i < batchesArray.length;i++){
batchesArray[i] = new int[batchesList.get(i).size()];
for (int j = 0; j < batchesArray[i].length; j++) {
batchesArray[i][j] = batchesList.get(i).get(j);
}
}
return batchesArray;
})
.subscribe(batchesArray -> System.out.println(Arrays.deepToString(batchesArray)));
Output:
[[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30], [31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60], [61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90], [91, 92, 93, 94, 95, 96, 97, 98, 99, 100]]
[[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30], [31, 32, 33, 34, 35, 36, 37, 38, 39, 40]]
[[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30], [31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60], [61, 62, 63, 64, 65, 66, 67, 68, 69, 70]]

How can I create an array from a method with ruby

How can I make an array of 30 min intervals to 8 hours. so this ish:
[30, 60, 90, all-the-way-to, 480]

You can use a Range and the step method, then convert it to an Array:
(30..480).step(30).to_a
The result is:
[30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330, 360, 390, 420, 450, 480)

Your arguments are
increment = 30
duration = 480 # 8*60
You could use
increment.step(by: increment, to: duration).to_a
#=> [ 30, 60, 90, 120, 150, 180, 210, 240,
# 270, 300, 330, 360, 390, 420, 450, 480]
which reads well. Numeric#step, when used without a block, returns an enumerator, which is why .to_a is needed.

I came up with this, but #infused answer is way better.
a = (1..16).to_a.map{|i| i*30 }

Option selecting (Enumerable#select) from the range:
stop = 480
step = 30
(step..stop).select { |n| n % step == 0 }
#=> [0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330, 360, 390, 420, 450, 480]

Why won't ruby-mcrypt accept an array as a key?

Hello I am having trouble encrypting using an array as the key and the value with the ruby-mcrypt gem. The gem lets me use an array for the key fine, cipher = Mcrypt.new("rijndael-256", :ecb, secret) works. But it will give me an error when I try to encrypt. I've tried many things but no luck. Does anyone know if Mcrypt just doesn't like encrypting with an array?
require 'mcrypt'
def encrypt(plain, secret)
cipher = Mcrypt.new("rijndael-256", :ecb, secret)
cipher.padding = :zeros
encrypted = cipher.encrypt(plain)
p encrypted
encrypted.unpack("H*").first.to_s.upcase
end
array_to_encrypt = [16, 0, 0, 0, 50, 48, 49, 55, 47, 48, 50, 47, 48, 55, 32, 50, 50, 58, 52, 54, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
key_array = [65, 66, 67, 68, 49, 50, 51, 52, 70, 71, 72, 73, 53, 54, 55, 56]
result = encrypt(array_to_encrypt, key_array)
p "RESULT IS #{result}"
The output is as follows:
Mcrypt::RuntimeError: Could not initialize mcrypt: Key length is not legal.
I traced this error to here in the ruby-mcrypt gem but don't understand it enough to figure out why I am getting the error message. Any help or insights would be amazing. Thanks!

The library doesn't support arrays. You'll need to use Strings instead:
def binary(byte_array)
byte_array.pack('C*')
end
array_to_encrypt = [16, 0, 0, 0, 50, 48, 49, 55, 47, 48, 50, 47, 48, 55, 32, 50, 50, 58, 52, 54, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
key_array = [65, 66, 67, 68, 49, 50, 51, 52, 70, 71, 72, 73, 53, 54, 55, 56]
result = encrypt(binary(array_to_encrypt), binary(key_array))
p "RESULT IS #{result}"

How to add an array to a two dimensional array

I want to add an array to a two dimensional array like this:
arrays = [[8300, 6732, 4101, 3137, 3097], [1088, 647, 410, 138, 52], [623, 362, 191, 25, 0]]
new_array = [10, 100, 1000]
arrays.map.with_index{|v,i| v << new_array[i]}
# => [[8300, 6732, 4101, 3137, 3097, 10], [1088, 647, 410, 138, 52, 100], [623, 362, 191, 25, 0, 1000]]
It works well, but I want to know if there is more simpler way to accomplish this behavior.
I appreciate any suggestion.

arrays.zip(new_array).map(&:flatten)
# => [[8300, 6732, 4101, 3137, 3097, 10], [1088, 647, 410, 138, 52, 100], [623, 362, 191, 25, 0, 1000]]

You can use zip:
arrays.zip(new_array).each { |arr, item| arr << item }
arrays
# => [[8300, 6732, 4101, 3137, 3097, 10], [1088, 647, 410, 138, 52, 100], [623, 362, 191, 25, 0, 1000]]

Just a little extension to Santosh answer. If there are nested arrays and you want to the result to be as nested as in original arrays like
arrays = [[8300, [6732], 4101, [3137], 3097], [1088, [647], 410, 138, 52], [623, [362], 191, 25, 0]]
new_array = [10, [100], 1000]
required_answer = [[8300, [6732], 4101, [3137], 3097, 10], [1088, [647], 410, 138, 52, 100], [623, [362], 191, 25, 0, 1000]]
then you can use
arrays.zip(new_array).map{|x| x.flatten(1)}
this will flatten the array to one level.

Issue with random mutation hill climbing

Hi I'm trying to write some simple code to use random mutation hill climbing for the travelling salesman problem. I have created a Tour class as such:-
import java.util.ArrayList;
import java.util.Collections;
public class Tour
{
private ArrayList<Integer> tour;
// Specified tour
public Tour(ArrayList<Integer> tour) { this.tour = tour; }
// Random tour
public Tour(int size)
{
// Initalize tour with size
tour = new ArrayList<Integer>(size);
// Add integers up to size into ArrayList
for (int i=0; i<size; ++i) {tour.add(i);}
// Shuffle ArrayList
Collections.shuffle(tour);
}
ArrayList<Integer> getTour() {return tour;}
void printTour()
{
for (int i=0; i<tour.size(); ++i)
{
System.out.print(tour.get(i) + ", ");
}
}
// Get the distance between all tour stops using a set of distances
double getFitness (double[][] distances)
{
double s = 0;
for (int i=0; i<tour.size()-1; ++i)
{
int a = tour.get(i);
int b = tour.get(i+1);
s += distances[a][b];
}
int start_city = tour.get(0);
int end_city = tour.get(tour.size()-1);
s += distances[end_city][start_city];
return s;
}
// Makes a small change to the tour
void smallChange()
{
// Change random index values to swap
int indexfirst = CS2004.UI(0, tour.size()-1);
int indexsecond = CS2004.UI(0, tour.size()-1);
// Checks to make sure index values are not the same
while (indexsecond == indexfirst)
{
indexsecond = CS2004.UI(0, tour.size()-1);
}
// Store city value in temp variable
int indexTemp = tour.get(indexfirst);
// Swap values
tour.set(indexfirst, tour.get(indexsecond));
tour.set(indexsecond, indexTemp);
}
}
My RMHC method looks like this:-
public static Tour RMHC(double[][] distances, int iter)
{
Tour sol = new Tour(distances.length);
double oldFitness;
double fitness = 0;
Tour oldSol=null;
for (int i=0;i<iter;i++)
{
oldSol = null;
// Make old solution equal to solution before change
oldSol = new Tour(sol.getTour());
System.out.println(oldSol.getTour());
// Calculate old fitness for comparison
oldFitness = sol.getFitness(distances);
// Change solution slightly
sol.smallChange();
// Calculate new fitness
fitness = sol.getFitness(distances);
/* Compare new fitness to old fitness
* set solution back to old solution and fitness to old fitness if
* new solution is not better */
System.out.println(oldFitness + " " + fitness);
if (fitness > oldFitness) {System.out.println(oldSol.getTour()); System.out.println(sol.getTour()); sol = null; sol = new Tour(oldSol.getTour()); fitness = oldFitness;}
// Print iteration number and new fitness
System.out.println("Iteration " + (i+1) + ", fitness: " + sol.getFitness(distances));
}
return(sol);
}
The problem I'm having is that when I call my smallChange method in the RMHC it seems to change the Tour for both the old solution and the new solution. I ran this for a few iterations on a 48 size dataset and got the following output:-
[11, 6, 13, 37, 23, 45, 34, 25, 16, 39, 5, 35, 31, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 22, 44, 7, 24, 43, 14, 41, 1, 38, 40]
155843.9387676824 159088.1701641078
[31, 6, 13, 37, 23, 45, 34, 25, 16, 39, 5, 35, 11, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 22, 44, 7, 24, 43, 14, 41, 1, 38, 40]
[31, 6, 13, 37, 23, 45, 34, 25, 16, 39, 5, 35, 11, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 22, 44, 7, 24, 43, 14, 41, 1, 38, 40]
Iteration 1, fitness: 159088.1701641078
[31, 6, 13, 37, 23, 45, 34, 25, 16, 39, 5, 35, 11, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 22, 44, 7, 24, 43, 14, 41, 1, 38, 40]
159088.1701641078 144709.1336957683
Iteration 2, fitness: 144709.1336957683
[31, 6, 13, 37, 7, 45, 34, 25, 16, 39, 5, 35, 11, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 22, 44, 23, 24, 43, 14, 41, 1, 38, 40]
144709.1336957683 143387.5110957744
Iteration 3, fitness: 143387.5110957744
[31, 6, 13, 37, 7, 45, 22, 25, 16, 39, 5, 35, 11, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 34, 44, 23, 24, 43, 14, 41, 1, 38, 40]
143387.5110957744 143565.3842060348
[31, 6, 13, 37, 7, 45, 22, 25, 16, 39, 5, 35, 14, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 34, 44, 23, 24, 43, 11, 41, 1, 38, 40]
[31, 6, 13, 37, 7, 45, 22, 25, 16, 39, 5, 35, 14, 9, 27, 0, 10, 42, 30, 28, 4, 12, 33, 36, 2, 21, 17, 29, 18, 20, 32, 3, 15, 47, 26, 19, 46, 8, 34, 44, 23, 24, 43, 11, 41, 1, 38, 40]

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