How to sort an array based on the numeric order of another array?

Question

EDIT : This is all done in C.

Let's say I have the two following arrays :

int numFields[] = {5, 1, 3, 2, 7}
char charFields[] = {'a' , 'b', 'c', 'd', 'e'}

I want to sort numFields numerically and have charFields resorted to match the new order of numFields such that :

int numFields[] = {1, 2, 3, 5, 7}
char charFields[] = {'b', 'd', 'c', 'a', 'e'}

I know that is possible to use qsort to sort numFields numerically, but is it possible to sort charFields to match the index changes of numFields? Is there a built in function or do I have to make my own implementation?

Thanks

@MarounMaroun what, and re-write the whole C project in Java? — Joe
– Joe, Commented Mar 31, 2014 at 12:47
Not directly - you would need to sort an index and then use that index to re-order the the original arrays. — Paul R
– Paul R, Commented Mar 31, 2014 at 12:50
Sort an array of indices from 0 to n-1 using the numFields array in the comparator and then reorder the charFields based on the indices. — George
– George, Commented Mar 31, 2014 at 12:50
The quicksort algorithm is very simple to implement. Obviously, the implemented version of the C standard library is not going to let you track the changed indexes, so, I recommend you to implement your own sort algorith to deal with it. — adripanico
– adripanico, Commented Mar 31, 2014 at 12:50
One approach would be to write your own implementation. which compares only numFields but swaps both numFields and charFields items. The other one would be rebuilding data to the array of structs { int num; char ch;}, then compare only num filed of struct. Thera are more... — CiaPan
– CiaPan, Commented Mar 31, 2014 at 12:52

Community · Accepted Answer · 2017-05-23 11:49:53Z

3

qsort lets you specify your own compare function to specify on what criteria the array should be sorted. It lets you sort an array of any type (can be int, can be struct) as long as you know the size of the objects you're sorting. Your best bet will be to create a struct pair { int numValue; char charValue } to represent the pair. You can

write a function to accept numFields and charFields and return an array of pair.
write a compare function, using this question and answers for reference. Other code examples here.
call qsort on your array of pairs and your comparison function
write a function to transform the array of pairs back to charFields.

edited May 23, 2017 at 11:49

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answered Mar 31, 2014 at 12:50

Joe

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Comments

H_squared · Accepted Answer · 2014-03-31 12:50:58Z

0

simply declare a struct array with each element holding the number as well as the letter corresponding to it. Then sort the array according to the numbers

or use qsort with a specific call back function to do what you need.

answered Mar 31, 2014 at 12:50

H_squared

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Comments

QuentinUK · Accepted Answer · 2014-03-31 13:37:22Z

#include <stdio.h>
#include <stdlib.h>

int numFields[] = {5, 1, 3, 2, 7};
char charFields[] = {'a' , 'b', 'c', 'd', 'e'};
// temporary arrays for sorted result   
int numFields2[5];
int charFields2[5];
// an index for sorting
int idx[] = {0, 1, 2, 3, 4};
// A cmompare function compares the numFields using the index values
int compar(const void* a,const void* b){
     return numFields[*(int*)a]-numFields[*(int*)b];
}

int main(void) {
    // sort the index values using the comapare function
    qsort(idx, 5, sizeof(int), compar);
    // use the sorted index to copy the values in the new sort order
    int i;
    for(i=0;i<5;i++){
      numFields2[i] = numFields[idx[i]];
      charFields2[i] = charFields[idx[i]];
     }
     // Copy result to original arrays
     for(i=0;i<5;i++){
        numFields[i] = numFields2[i];
        charFields[i] = charFields2[i];
     }
    return 0;
}

i'm PosSible · Accepted Answer · 2014-03-31 12:50:34Z

-1

Here i try to devlop bubble sort program try using it.,

int temp;
char a;
for(i=0;i<no;i++)
    {
        for(j=i;j<no;j++)
        {
            if(numFields[i] > numFields[j])
            {
                temp=numFields[i];
                numFields[i]=numFields[j];
                numFields[j]=temp;


                a=charFields[i];
                charFields[i]=charFields[j];
                charFields[j]=a;
            }
        }
    }

answered Mar 31, 2014 at 12:50

i'm PosSible

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6 Comments

i'm PosSible Over a year ago

why not?? using this he can make his own implementation.

Paul R Over a year ago

-1: bubble sort is very inefficient - also the code above is buggy.

i'm PosSible Over a year ago

ya that’s why I specify ..i know bubble sort is not proper .

i'm PosSible Over a year ago

he want own implementation code that's why i give this type of answer

Joe Over a year ago

I didn't down-vote, but it's a very bad idea to re-implement sorting algorithms unless you really need to. Even in the simplest implementation it's easy to introduce bugs.

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