iteration - w3toppers.com

Remove elements from collection while iterating

Let me give a few examples with some alternatives to avoid a ConcurrentModificationException. Suppose we have the following collection of books List<Book> books = new ArrayList<Book>(); books.add(new Book(new ISBN(“0-201-63361-2”))); books.add(new Book(new ISBN(“0-201-63361-3”))); books.add(new Book(new ISBN(“0-201-63361-4”))); Collect and Remove The first technique consists in collecting all the objects that we want to delete (e.g. using an … Read more

Iterating on a file doesn’t work the second time

Yes, that is normal behavior. You basically read to the end of the file the first time (you can sort of picture it as reading a tape), so you can’t read any more from it unless you reset it, by either using f.seek(0) to reposition to the start of the file, or to close it … Read more

Iterating through a range of dates in Python

Why are there two nested iterations? For me it produces the same list of data with only one iteration: for single_date in (start_date + timedelta(n) for n in range(day_count)): print … And no list gets stored, only one generator is iterated over. Also the “if” in the generator seems to be unnecessary. After all, a … Read more

Can every recursion be converted into iteration?

Can you always turn a recursive function into an iterative one? Yes, absolutely, and the Church-Turing thesis proves it if memory serves. In lay terms, it states that what is computable by recursive functions is computable by an iterative model (such as the Turing machine) and vice versa. The thesis does not tell you precisely … Read more

Ways to iterate over a list in Java

The three forms of looping are nearly identical. The enhanced for loop: for (E element : list) { . . . } is, according to the Java Language Specification, identical in effect to the explicit use of an iterator with a traditional for loop. In the third case, you can only modify the list contents … Read more

How can you iterate over the elements of an std::tuple?

I have an answer based on Iterating over a Tuple: #include <tuple> #include <utility> #include <iostream> template<std::size_t I = 0, typename… Tp> inline typename std::enable_if<I == sizeof…(Tp), void>::type print(std::tuple<Tp…>& t) { } template<std::size_t I = 0, typename… Tp> inline typename std::enable_if<I < sizeof…(Tp), void>::type print(std::tuple<Tp…>& t) { std::cout << std::get<I>(t) << std::endl; print<I + 1, … Read more

How to iterate over a JavaScript object?

For most objects, use for .. in : for (let key in yourobject) { console.log(key, yourobject[key]); } With ES6, if you need both keys and values simultaneously, do for (let [key, value] of Object.entries(yourobject)) { console.log(key, value); } To avoid logging inherited properties, check with hasOwnProperty : for (let key in yourobject) { if (yourobject.hasOwnProperty(key)) … Read more

Way to go from recursion to iteration

Usually, I replace a recursive algorithm by an iterative algorithm by pushing the parameters that would normally be passed to the recursive function onto a stack. In fact, you are replacing the program stack by one of your own. var stack = []; stack.push(firstObject); // while not empty while (stack.length) { // Pop off end … Read more

Does pandas iterrows have performance issues?

Generally, iterrows should only be used in very, very specific cases. This is the general order of precedence for performance of various operations: 1) vectorization 2) using a custom cython routine 3) apply a) reductions that can be performed in cython b) iteration in python space 4) itertuples 5) iterrows 6) updating an empty frame … Read more