sorting arrays

**bradleyd** · 06-17-2008

hello everyone,

I was wondering if there is way to sort two different arrays of different data types without struct's.
For example lets say you have an array of doubles that represent rainfall for each month of the year. [0] representing January's rainfall amount, etc... Then I have an array of char's with the names of the months. [0] representing "January". Now I sort the rainfall in descending order, how do I get the char array to stay in sync with the rainfall array. I was planning on using a selection method to sort the rainfall amounts, but I can't pass it a double array and a char array.
I know I could create another array of int's and use a selection method to sort rainfall and int's 1-12 to represent the months. Then I could pass this to a switch statement or loop to display the months rainfall. This way seems to show my inexperience. I know there has to be a way to sort them without any special libs.

thanks for your time,
Brad

**laserlight** · 06-17-2008

I would create say, a MonthlyRainfall class (or struct) that contains the month name and the rainfall for that month. Then I define operator< (or a function object predicate) that sorts MonthlyRainfall objects by the rainfall. After that, I apply std::sort and my work is done.

**bradleyd** · 06-17-2008

thanks for the reply. Unfortunately I can't use struct's. I have to do this with just arrays, or vector's.

**tabstop** · 06-17-2008

So, don't sort the data themselves, sort the indexes. So your double array won't change; your char * array won't change, but you'll have index[0]=6, index[1]=4, and so on.

**laserlight** · 06-17-2008

Unfortunately I can't use struct's. I have to do this with just arrays, or vector's.

Why? It is generally not so good to maintain parallel containers.

**bradleyd** · 06-17-2008

this is a class assignment and we have not gotten to struct's yet.

**bradleyd** · 06-17-2008

Here is the osrt method I am using. I created an array of int's to try it out for now.
I am passing it month[] which is an array of int's(1-12) and the rainfall amounts the user has entered, plus the size of the arrays.

Code:

void dualSort(int month[], double precip[], int size) {
	
	int start, maxIndex, tempMonth;
	double maxAmount;
	
	for (start = 0; start < (size - 1); start++) {
		maxIndex = start;
		maxAmount = precip[start];
		tempMonth = month[start];
		for (int index = start + 1; index < size; index++) {
			if (precip[index] > maxAmount) {
				maxAmount = precip[index];
				tempMonth = month[index];
				maxIndex = index;
			}
		}
		precip[maxIndex] = precip[start];
		month[maxIndex] = month[start];
		precip[start] = maxAmount;
		month[start] = tempMonth;
	}
}

**bradleyd** · 06-17-2008

So, don't sort the data themselves, sort the indexes. So your double array won't change; your char * array won't change, but you'll have index[0]=6, index[1]=4, and so on.

Will the data still come out in descending order? I gues I am unsure what you mean.
Thanks for the reply.

**laserlight** · 06-17-2008

Will the data still come out in descending order? I gues I am unsure what you mean.

Of course, if you access the indices in sorted order. Alternatively, you can sort both the vectors at once, i.e., whenever you copy or swap a double that represents a rainfall amount, you copy or swap the corresponding string that represents the month name.

**bradleyd** · 06-17-2008

I will give it a try and post back. Thanks again.

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