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C++ STL Sort a map based on values instead of keys

To use a map in a C++ program, the map library has to be included with an include directive. To work with C++ map, we create an iterator to iterate over the elements. Create a map named my_map whose keys will be strings and values integers. Create a map named Students whose keys will be integers and values strings.

A map consists of key/value pairs. The sorting can be ascending amp definition seo glossary or descending. Sorting in a map is not always straightforward.

This pointer can point in either direction of the container and hence it is bidirectional. In above example we sorted the contents of a map in ascending order of value. If you want to sort the map contents in descending order then use following lambda function in above example i.e. Then we will copy the elements from map to set and it will store them in sorted order of values. Unsorted by string literals, but sorted by pointers.

In this example, notice that all keys are different and unique, but in the value column, the value 20 is the same for the key Computer_Science and Physics. If you prefer, you can use a char that’s signed and use it to index off of a pointer that points to the middle of the array. There’s no need to return 0; from main–the compiler will do that automatically if you just let control flow off the end of main. In addition, the array will almost certainly be quite a bit faster than either a map or unordered_map. I know we should not say thanks and become sentimental, but this was a very thorough and nice review of my code. C++11 provides another solution to the same problem, namely a lambda expression.

Print the values of the map m on the console. The “\t” character creates a horizontal space between each key and its corresponding value. In contrast, the “\n” character moves the mouse cursor to the next line after every iteration.

HashMap allows a single null key and multiple null values. TreeMap does not allow null keys but can have multiple null values. HashMap allows heterogeneous elements because it does not perform sorting on keys. TreeMap allows homogeneous values as a key because of sorting. To reverse sort map entries, pass Collections.

Passing small trivially-copyable types by value is The Right Thing. Not that it matters if the callee is such a simple function-object and the call thus gets inlined. Regarding the best container to use for calculating frequencies, it is hard to beat a plain native array. In this article we will discuss how to sort a map by value in both ascending and descending order.

This function returns a pointer pointing corresponding to the key or will point before the key value. This function returns a pointer pointing corresponding to the key or will point after the key value. This function returns a key and the element corresponding to it. Empty() function is a member function of C++ Map with boolean datatype. It checks if the container is empty or not.