Sorting a float array
How do you use the sort(float[] a), i want to find the smallest number in my float array? help would be appreciated thanks.
float smallest=0;
float[] smallestCostArray = new float[25];
for(int i=0;i<stageSize;i++)
if(smallest < smallestCostArray){
smallest = smallestCostArray[i];
this is my code for trying to find the smallest , but i get a "operator < cannot be applied to float,float[]" error when trying to compile.
Message was edited by:
dets00b
Message was edited by:
dets00b
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I found that for primitive types such as int, float, etc., algorithm for sort is a tuned quicksort. However the algorithm for sorting an object array is a modified merge sort according to the java API. What is the purpose of using two different sorting strategy?
Thanks.The language knows how to compare two ints, two doubles, etc. For Object arrays, however, it's not a simple matter of comparing two reference values as ints or longs. We're not comparing the references. We have to compare the objects, according to the class's compareTo() method (if it implements Comparable) or a provided Comparator. The size of an int is known, fixed, and small. The size of an object is unknown, variable, and essentially unbounded. I don't know for sure that that difference is what drove the different approaches, but it is a significant difference, and mergesort is better suited to use cases where we can't fit the entire array into memory at one time. It seems reasonable that we'd get better locality of reference (fewer cache misses, less need to page) with an array of ints than with an array of objects.
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Newbie trying to sort 2D string array
Dear all,
After read some book chapters, web sites including this, I still don't get the point.
If I have a file like,
1 aaa 213 0.9
3 cbb 514 0.1
2 abc 219 1.3
9 bbc 417 10.4
8 dee 887 2.1
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and I load into memory as a String[][]
here comes the problem, I sort by column 1 (aaa,...,bba) using an adaptation of the Quicksort algorithm for 2D arrays
* Sort for a 2D String array
* @param a an String 2D array
* @param column column to be sort
public static void sort(String[][] a, int column) throws Exception {
QuickSort(a, 0, a.length - 1, column);
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static void QuickSort(String[][] a, int lo0, int hi0, int column) throws Exception {
int lo = lo0;
int hi = hi0;
int mid;
String mitad;
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/* Arbitrarily establishing partition element as the midpoint of
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----- end of the code --------
if I call this from the main module like this
import MyUtil.*;
public class kaka
public static void main(String[] args) throws Exception
String[][]a = MyUtil.fileToArray("array.txt");
MyMatrix.printf(a);
System.out.println("");
MyMatrix.sort(a,1);
MyMatrix.printf(a);
System.out.println("");
MyMatrix.sort(a,3);
MyMatrix.printf(a);
for the first sorting I get
1 aaa 213 0.9
2 abc 219 1.3
9 bba 111 7.1
9 bbc 417 10.4
3 cbb 514 0.1
8 dee 887 2.1
(lexicographic)
but for the second one (column 3) I get
3 cbb 514 0.1
1 aaa 213 0.9
2 abc 219 1.3
9 bbc 417 10.4
8 dee 887 2.1
9 bba 111 7.1
this is not the order I want to apply to this sorting, I would like to create my own one. but or I can't or I don't know how to use a comparator on this case.
I don't know if I am rediscovering the wheel with my (Sort String[][], but I think that has be an easy way to sort arrays of arrays better than this one.
I've been trying to understand the Question of the week 106 (http://developer.java.sun.com/developer/qow/archive/106/) that sounds similar, and perfect for my case. But I don't know how to pass my arrays values to the class Fred().
Any help will be deeply appreciated
Thanks for your help and your attention
Pedropublic class StringArrayComparator implements Comparator {
int sortColumn = 0;
public int setSortColumn(c) { sortColumn = c; }
public int compareTo(Object o1, Object o2) {
if (o1 == null && o2 == null)
return 0;
if (o1 == null)
return -1;
if (o2 == null)
return 1;
String[] s1 = (String[])o1;
String[] s2 = (String[])o2;
// I assume the elements at position sortColumn is
// not null nor out of bounds.
return s1[sortColumn].compareTo(s2[sortColumn]);
// Then you can use this to sort the 2D array:
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String[][] array = ...
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Object[String[], int[]]
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Hi,
I have some problems with generating unique hash codes for float arrays.
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System.out.println(Arrays.hashCode(new float[]{0,1,2,3,6,9}) == Arrays.hashCode(new float[]{0,1,3,6,8,9}));Does anyone have an idea how to generate a truly unique hashcode for float arrays?
Thanks for your help,
DieterJoachimSauer wrote:
dkleinrath wrote:
JoachimSauer wrote:
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public class Input3
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private static int StringNum = -1;
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Sorting between multiple arrays.
I thought that I had posted this yesterday; however as I can not find my post...
I need assistance with part of a project where I need to sort between multiple arrays; using one of the columns as the sort criteria. The arrays contain integers, strings, and doubles; however I would like to sort and display the arrays alphabetically using the string column. I was told that a bubble array may work, however as I can not find specific information on the use of a bubble array, I really don't know where to start. The arrays look like the following:
productArray[0] = new Product(1, "binder ", 15, 1.5, 0, 0);
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DmanThank you for your assistance.
The site that I found to be most helpful was the http://www.onjava.com/lpt/a/3286 site; however I am still experiencing problems. I have added code to the program as noted below:
public class Inventoryprogrampart3
/** Creates a new instance of Main */
* @param args the command line arguments
public static void main(String[] args)
// create Scanner to obtain input from command window
java.util.Scanner input = new java.util.Scanner( System.in );
double totalInventoryValue = 0;
NumberFormat nf = NumberFormat.getCurrencyInstance();
System.out.println(); // Displays a blank line
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System.out.println( " ----------------------------------------- " ); // displays a line of characters
System.out.println(); // Displays a blank line
System.out.println( "This program will output an office supply inventory" ); // Display the string
System.out.println( "listing that includes item numbers for the" ); // Display the string.
System.out.println( "inventoried products, the items product names, the" ); // Display the string.
System.out.println( "quantity of each product in stock, the unit price" ); // Display the string
System.out.println( "for each product, the total value of each products" ); // Display the string
System.out.println( "inventory, and a total value of the entire inventory." ); // Display the string
System.out.println(); // Displays a blank line
System.out.println( "*****************************************************" ); // Displays a line of characters
System.out.println(); // Displays a blank line
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// adds data to the 7 arrays
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productArray[2].setitemPrice(.25);
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productArray[5].setitemNumber(7);
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productArray[6].setitemNumber(6);
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productArray[6].setitemQuantity(13);
productArray[6].setitemPrice(1.25);
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System.out.println( "-----------------------------------------------------" ); // Displays a line of characters
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int itemQuantity = products.getitemQuantity();
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Arrays.sort(productArray);
System.out.println( "-----------------------------------------------------" ); // Displays a line of characters
System.out.println(); // Displays a blank line
System.out.println( "Inventory listing after being sorted by product name:" );
System.out.println(); // Displays a blank line
System.out.println( "Item #"+"\t"+"Product Name"+"\t"+"Stock"+"\t"+"Price"+"\t"+"Total Value"); // Displays a header line for the inventory array display
System.out.println(); // Displays a blank line
System.out.println( "-----------------------------------------------------" ); // Displays a line of characters
for(int i=0; i <= 6; i++)
totalInventoryValue = totalInventoryValue + productArray[i].getinventoryValue(); // calculates the total value of the entire products inventory
System.out.println( productArray[i].getitemNumber() +"\t"+ productArray[i].getproductName() +"\t"+"\t"+ productArray[i].getitemQuantity() +"\t"+ nf.format(productArray[i].getitemPrice()) +"\t"+ nf.format(productArray[i].getinventoryValue()) );
}// end for
System.out.println(); // Displays a blank line
System.out.println( "The total value of the entire inventory is: " + nf.format(totalInventoryValue) ); // Displays the entire inventory value
System.out.println(); // Displays a blank line
System.out.println( "*****************************************************" ); // Displays a line of characters
} // end public static void main
}// end public class Inventoryprogrampart3 main
The following utilities have been set:
import java.io.*;
import java.text.*;
import java.util.Scanner;
import java.util.*;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.Comparator;
The program compiles, however when I try to run the program I receive the following error (which outputs about 1/2 way through the program:
Exception in thread "main" java.lang.ClassCastException: Product can not be cast to java language comparable.
(along with a listing of other errors - I can't even get my cut and paste to work on my command prompt window).
I've tried about 50 different iterations and nothing seems to work. -
How to read binary file into a 2D float array??
Hi All,
I really need help to get this one as I am stuck and can't seem to find any way out of it. I am given a '.dat' file that has float values in it. I want to read this file in java and put it in a 2D float array. The file has basically a matrix of float values. What I want to do is to read this binary file and put all its data into 2D float array (float [] []) so that I can use it in my program. Is there a way to read file like this? I did find a similar matlab code (below) but cant seem to find anything in java and i really want to do this in java only.. I will appreciate ur help in this one.
thanks very much
Nitya
fid = fopen('datafile.dat');
A = fread(fid,[50 50],'float32');
fclose(fid);I shud have shown the two ways that i Already tried. here they are..
first one using DataInputStream and then trying to readFloat()
DataInputStream dis = ....
Float f = dis.readFloat();This code gives code gives me some random values like this.. (i had a loop)
5.8758974E-14
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1.5724557E-30
1.06822824E14
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3.43829601E13
Other way i tried was this.. which seems right but here i have to convert byte to float and i thnk that code is giving some different results (slightly different float values) not sure why....may be my indexing of the array is wrong to make it a matrix.. or something else...
is.read(bytes, offset....);
int cnt = 0;
int j = 0;
for (int start = 0; start < offset; start = start + 4) {
if(j<50){
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System.out.println(cnt + "-" + j + " = " + myarray[cnt][j]);
j++;
}else{
if(cnt < 50){
cnt++;
j = 0;
}else{
break;
public float arr2float (byte[] arr, int start) {
int i = 0;
int len = 4;
int cnt = 0;
byte[] tmp = new byte[len];
for (i = start; i < (start + len); i++) {
tmp[cnt] = arr;
cnt++;
int accum = 0;
i = 0;
for ( int shiftBy = 0; shiftBy < 32; shiftBy += 8 ) {
accum |= ( (long)( tmp[i] & 0xff ) ) << shiftBy;
i++;
return Float.intBitsToFloat(accum);
Not sure if i am missing some other way to do this... -
How do I convet C Float array to Java Float Array.
Hi All,
I am using some C function in the JNI which will return Float array.
How do I convert the Float C array elements to jfloatArray elemets. And my native method implementation should return jfloatArray.
If any one of you have the sample code please send reply.
regards
Ravi Kumarto return the c array to jfloat array do the following:
ur function should have a return type of jfloat
this is for c++::
jfloatArray ret = (jfloatArray)env->NewFloatArray(length of the array);
env->SetFloatArrayRegion(ret,index,number of retunrs,jfloat *);
for c u just have to include the env variable
jfloatArray ret = (jfloatArray)env->NewFloatArray(env,length of the array);
return ret;
this will work when u give the array indexes properly.
regards
vidhya
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