There’s a good article on the topic in the Python wiki: Why Lists Can’t Be Dictionary Keys. As explained there: What would go wrong if you tried to use lists as keys, with the hash as, say, their memory location? It can be done without really breaking any of the requirements, but it leads to … Read more
Named tuples are basically easy-to-create, lightweight object types. Named tuple instances can be referenced using object-like variable dereferencing or the standard tuple syntax. They can be used similarly to struct or other common record types, except that they are immutable. They were added in Python 2.6 and Python 3.0, although there is a recipe for … Read more
In C++17 you can do this: std::apply(the_function, the_tuple); This already works in Clang++ 3.9, using std::experimental::apply. Responding to the comment saying that this won’t work if the_function is templated, the following is a work-around: #include <tuple> template <typename T, typename U> void my_func(T &&t, U &&u) {} int main(int argc, char *argv[argc]) { std::tuple<int, float> … Read more
It is only required for single-item tuples to disambiguate defining a tuple or an expression surrounded by parentheses. (1) # the number 1 (the parentheses are wrapping the expression `1`) (1,) # a 1-tuple holding a number 1 For more than one item, it is no longer necessary since it is perfectly clear it is … Read more
Try using the key keyword with sorted(). sorted([(‘abc’, 121),(‘abc’, 231),(‘abc’, 148), (‘abc’,221)], key=lambda x: x[1]) key should be a function that identifies how to retrieve the comparable element from your data structure. In your case, it is the second element of the tuple, so we access [1]. For optimization, see jamylak’s response using itemgetter(1), which … Read more
What is the equivalent of the C++ Pair in Java?
Tuples are compared position by position: the first item of the first tuple is compared to the first item of the second tuple; if they are not equal (i.e. the first is greater or smaller than the second) then that’s the result of the comparison, else the second item is considered, then the third and … Read more
In Python 2: >>> list_a = [1, 2, 3, 4] >>> list_b = [5, 6, 7, 8] >>> zip(list_a, list_b) [(1, 5), (2, 6), (3, 7), (4, 8)] In Python 3: >>> list_a = [1, 2, 3, 4] >>> list_b = [5, 6, 7, 8] >>> list(zip(list_a, list_b)) [(1, 5), (2, 6), (3, 7), (4, … Read more
Apart from tuples being immutable there is also a semantic distinction that should guide their usage. Tuples are heterogeneous data structures (i.e., their entries have different meanings), while lists are homogeneous sequences. Tuples have structure, lists have order. Using this distinction makes code more explicit and understandable. One example would be pairs of page and … Read more
sorted_by_second = sorted(data, key=lambda tup: tup[1]) or: data.sort(key=lambda tup: tup[1]) # sorts in place The default sort mode is ascending. To sort in descending order use the option reverse=True: sorted_by_second = sorted(data, key=lambda tup: tup[1], reverse=True) or: data.sort(key=lambda tup: tup[1], reverse=True) # sorts in place