perl - How does the grep operator work? -


I have an array and a hash. I want to match the keys of the head with the key of hash.

I got an expression to fix all the keys matching the array. It works, but I'm not sure I understood how it works. Can you explain what happens after grep

array @text and hash % sys already Is defined only. 

  My @new_array = grep {$ sys {$ _} is present? $ sys {$ _}: 0} @text;    
 
 
 The code you got is more complex This could be / *:  
  My @new_array = grep {$ sys {$ _}} @text; The   
  grep  function processes a list - the contents of the  @text  array - in a new list containing only the element Where the expression in the middle evaluates a true value, the default value is set to every list item in exchange for the expression list content so that the default value is  $ _ .  
 In your example expression, a threesome operator ?  which evaluates the item before :  If the first part is true or the value after it is incorrect, in your case, it checks whether each key is % sys  is in hash, and hash evaluates a lookup of entry if it exists, or 0 (a wrong value) if it is not functionally within a  grep  Should be due to  $ sys {$ _}  because  undef  is that you have a non-denominator Key is also wrong. However, there is a caveat - if % sys  was tied to a pearl class and some hash functions were overridden, Different hash methods are called for  existing  and hash lookups. Therefore there can be a difference in performance or behavior in that scenario.

Comments

Post a Comment

Popular posts from this blog

c# - passing input text from view to contoller with FacebookContext using Facebook app -

I'm trying to pass an input text from the viewer to the controller in the Facebook Birthday app: Link to app: In the Home Controller [FacebookAuthorize ("email", "user_photos")] Public async Tasks & lt; ActionResult & gt; Index (FacebookContext reference) {if (ModelState.IsValid) {var user = waiting for reference. Client.Gate CurrentUserAsync & lt; MyAppUser & gt; (); View return (user); } See Return ("Error"); } [Http post] [facebook authorized ("email", "user_photo")) public async task & lieutenant; Actionsclass & gt; Index (string textile, facebookcontonte context) {if (ModelState.IsValid) {var user = wait context.Client.GetCurrentUserAsync & lt; MyAppUser & gt; (); // See my code, see the use of txt here (user); } See Return ("Error"); } View: @using facebookpostc.models @ Microsoft.AspNet.Mvc.Facebook.models using @ Microsoft.AspNet.Mvc. Facebook @model MyAppUser @ {ViewB...
Read more

ios - Does Core Data autoupdate a many to many relationship on saving -

I have used 2 database tables and core data / NSManagedObjects in SQLite: User is user_id name group (multiple groups) Group group_id title group members (multiple users) By using core data to save a group and adding users ( Add to group) as follows: group * cordata = zero; Cordata = [NSEntityDescription insertNewObjectForEntityForName: @ Managed Object Contains in "Groups": Reference]; Request = [NSFetchRequest fetchRequestWithEntityName: @ "user"]; Request.predicate = [NSPredicate predicateWithFormat: @ "user_id =% @", user_id]; Result = [reference executeFetchRequest: request error: & amp; Error]; CoreData.group_id = group_id Cordettitle = Title [Cordata AdGroupMailersObject: [Last objections result]]; Is it right to say that core data manages a user with multiple users and groups with the code above? Yes, if the relationships are in the form of each other's inverse relationship The inverse relationships are updated automaticall...
Read more

Calling a C++ function from C# by passing a string with variable size to it -

I am calling a string with a C + code and calling from the C # code. The C ++ function is responsible for filling the string material. The following code is: C #party: var abc = new string builder (4096); // will have to change this var result = Basic methods. SignCrcFile (ABC); C ++: bool __cdecl SignCrcFile (char * abc) {... char * tempStr = "hello all"; // for example // copy it to ABC string strcpy (ABC, tempStr); Back true; } The problem is that tempStr's size in the C ++ function is dynamic (the above assignment for TempStr is only an example). In such a case, it is not a hard code that the size of ABC string is in the size of 4096 bytes on the C #. The first solution can be a solution to create 2 functions on the C ++ side to get the size of the string. Then allocate that size using StringBuilder in the C # side then use the next function to bring the entire string from C ++ to the C #. But no suggestion this may not be the most optimal way? ...
Read more