iteration

问题 After a couple hours of research (on MSDN websites and so on) I didn't manage to find out why the generic Dictionary<TKey, TValue> does not provide a ForEach() method like List<T> does. Could someone please give me an explanation? (I know that it's not hard to implement it as an extension method, a great example can be seen here, I just was wondering whether there might be a particular reason why it's not provided by the .NET libraries in the first place.) Thanks in advance. 回答1: Because it's

问题 for (let x of a) does not work in IE11. Can I replace it by for (let x in a) ? for (let key in a) { s += key + ": " + a[key]; s += "<br />"; } for (let key of a) { s += key + ": " + a[key]; s += "<br />"; } 回答1: for...of is not supported in IE11 yet. You can use for..in to iterate over as it has the support from IE6. If you just want to add the key and value , you can use Object.keys and build the string that is needed. let f = ''; let s = ''; let a = { firstName: 'Hello', lastName: 'JS',

问题 This question already has answers here : how to read array of numbers from text file in python (2 answers) Closed 4 years ago . I'm aware that this may have been answered before but please check that other answers are relevant to this instance! I'm writing an array to a file as a string so that it can be stored when my script isn't running and be accessed again easily when run. When I then read this string out of the file again it is automatically read as a string. I can fix this with a for

问题 Consider a generator in Julia that if collected will take a lot of memory g=(x^2 for x=1:9999999999999999) I want to take a random small subsample (Say 1%) of it, but I do not want to collect() the object because will take a lot of memory Until now the trick I was using was this temp=collect((( rand()>0.01 ? nothing : x ) for x in g)) random_sample= temp[temp.!=nothing] But this is not efficient for generators with a lot of elements, collecting something with so many nothing elements doesnt

问题 import java.util.Scanner; public class Problem1{ public static void main(String[] args){ //input Scanner kb = new Scanner(System.in); String word,letter; int counter=0, match,value; word=kb.next(); word=word.toLowerCase(); letter=kb.next(); letter=letter.toLowerCase(); //loop for (int i=0;i<word.length();i++) if (word.charAt(i)==letter.charAt(0)){ counter++; match=i; System.out.print(match); } if (counter==0) System.out.print(-1); } } I must execute this program in Codio. This program will

问题 I have a list of over 100000 values and I am iterating over these values and checking if each one is contained in another list of random values (of the same size). I am doing this by using if item[x] in randomList . How efficient is this? Does python do some sort of hashing for each container or is it internally doing a straight up search of the other container to find the element I am looking for? Also, if it does this search linearly, then does it create a dictionary of the randomList and

问题 I am a JavaScript newbie. I'm trying to practice some sample JavaScript problems. I'm a little stuck when it comes to this question about iterating over arrays. Can anyone point me in the right direction? I am trying to take the values in oldArray , add 5 to each of them, and store in newArray . var oldArray = [12, 45, 6, 23, 19, 20, 20, 15, 30, 42]; var newArray = []; function plusFive(oldArray[i]) { for (var i = 0; i < oldArray.length; i++) { newArray.push(oldArray[i]) + 5) }; } } 回答1: Bug

问题 I have several lists and I need to do something with each possible combination of these list items. In the case of two lists, I can do: for a in alist: for b in blist: # do something with a and b However, if there are more lists, say 6 or 7 lists, this method seems reluctant. Is there any way to elegantly implement this iteration? 回答1: You could use itertools.product to make all possible combinations from your lists. The result will be one long list of tuple with an element from each list in

问题 I have several lists and I need to do something with each possible combination of these list items. In the case of two lists, I can do: for a in alist: for b in blist: # do something with a and b However, if there are more lists, say 6 or 7 lists, this method seems reluctant. Is there any way to elegantly implement this iteration? 回答1: You could use itertools.product to make all possible combinations from your lists. The result will be one long list of tuple with an element from each list in

问题 If I run the following code, it will print out 3 times duplicate, but when I remove the if statement inside the while loop (just to see how many times it will iterate) it starts an infinite loop. How does actually this hasNext() method working? I thought that will iterate only 5 times as I have 5 items in the list. public class ExerciseOne { public static void main(String []args){ String []colors = {"MAGENTA","RED","WHITE","BLUE","CYAN"}; List<String> list = new ArrayList<String>(); for