I have 4 values coming from json (name, ratings, reviews and Qualifications). I want to sort this data using name, reviews and qualifications one by one. But when I sort this data then remaining values are not changing in array.
Here is my code.
_arrOfDoc_name = [_arrOfDoc_name sortedArrayUsingSelector:#selector(localizedCaseInsensitiveCompare:)];
From comments:
I have to show four values on my screen which are coming from 4 different arrays. but when i sort one array then values of another arrays are not gng to sort and it displays wrong data on screen. how can i sort data of remaining arrays using its index path.
Ok, your comments explain what you're trying to do.
The best answer is to NOT use 4 different arrays. Restructure your data to have a single array that contains dictionaries. Then sort the array of dictionaries.
Failing that, you'll have to be clever. You might be able to create an array of indexes and sort that, or hand-write a sort routine that sorts all 4 arrays at once.
Related
I've got a value like so: #"2329300" and I've got a NSDictionary like so :{#"John Appleseed":[#"2329300",#"2342322",#"32i249"]}
How do I find the index of the key/value pair in the NSDictionary when I've only got a string value of the entire list that's known as the value. I'm assuming there's no duplicates in the dict.
I know that there's indexForObject on a NSArray but is there a similar thing for a dict?
I imagine it would look something like this:
[NSDictionary indexForValue:value]; // returns index number.
And even then the NSString doesn't match the value, so I'd need a workaround for that too.
You have a basic misunderstanding. Dictionaries are unordered collections. They do not have any particular order for their key/value pairs. You can't have indexes to the key/value pairs because that implies a fixed order.
Think of a dictionary as a bunch of kids milling around on a playground. You can call out a kid's name "Johnny, come here!" and fetch that kid (use a key to find an object) but what does order mean for kids that won't sit still?
You can create an array of the keys from a dictionary and sort that into a particular order (an alphabetical list of the kids on the playground) if that's what you want, or you can create an array of dictionaries, or an array of a custom data object that contains any arbitrary properties that you want.
EDIT:
For a table view, an array of dictionaries is probably a good choice. Each entry in the array contains a dictionary with all the settings for a cell in the dictionary. If you have a sectioned table view then you want an outer array for sections, containing inner arrays for the rows, and each entry in the inner array containing a dictionary.
I tend to prefer custom data objects to dictionaries though. (An object that just has properties for each setting I want.) That way the list of values and their types is crystal-clear and fairly self-documenting.
Is there a way to sum the values entered into a table view cell without using Core Data? I am currently using Parse. I guess a better question would be how can I get the sum using Parse? I'm really scratching my head on this one. Hand holding may be required.
You can probably use the Key-Value Coding collection operators. Suppose the row data for the table are a bunch of instances of class Entry and are collected in an NSArray named data. Further suppose each Entry object has an NSNumber property named cost and this is what you want to sum. Then you can do so as follows:
NSNumber *sum = [data valueForKeyPath:#"#sum.cost"];
Just to be clear: this does require that the values you wish to sum are properties of the objects that are backing each row.
This question already has answers here:
What's the difference between a dictionary and an array?
(6 answers)
Closed 10 years ago.
I'm in a dilemma in terms of which of the two I should use. I will be retrieving a group of data via a restful API (returns json) and I'm not sure how I should store them before I display it on my UI View Table.
eg.
{"Events":[{"Id":5,"Name":"Event 1 2013"},{"Id":6,"Name":"Event 2 2013"}]}
I've been reading tutorials and some would use NSMutableArrays while some would use NSMutableDictionary.
How should I go about it?
BTW: I'm displaying the data on UI View table that will redirect the user to another page when tapped and if they decide to go back will have to show the previous view without reloading (uses UinavigationController)
Thanks!
EDIT:
Also, just to give you an idea on what I'm trying to do. I'm trying to follow this tutorial on splitting the data I get into section headers. On this tutorial it's using NSDictionary.
http://www.icodeblog.com/2010/12/10/implementing-uitableview-sections-from-an-nsarray-of-nsdictionary-objects/
If I use NSArray, would that affect the performance?
In NSArray - every item in the collection has an integer index, so there is an explicit order to the items. When you're retrieving/replacing/removing the stored object from the NSARRY,you need to specify the corresponding object index of that stored object.
NSDictionary - derived from the word called entry. Each entry consists of one object that represents the key and a second object that is that key’s value. Within a dictionary, the keys are unique. That is, no two keys in a single dictionary are equal (as determined by isEqual:).When you're retrieving the object from the dictionary you need to specify the key value for the objectForKey
Whenever if you're parsing the plist then NSDictionary would be ideal.You can refer apple's document here for more explanation about NSDictionary.Happy coding :)
The lookup times on NSDictionaries are faster than on NSArrays. That's one of the main advantages. Here's a link to the Apple documentation.
Generally, if you need to access data in an indexed fashion (like you need to for rows in a table) then you should use an array because you can access any specific index using indexOfObject:
Now, if you have a lot of information for each row then you should have an array of either custom objects or an array of dictionaries.
Dictionary are always faster than Arrays. Dictionary maps keys to objects, just like a hash table. It's an associative array.
For searching some value you need to iterate for arrays, in dictionary you retrieve it by key.
If you want the collection to be in some sorted order or arrival order then Array is the proper type for you.
Dictionary lacks when you end up getting two same keys.
And I feel good to use arrays for tableViews as I can directly associate row to index.
Given two linked lists of integers. I was asked to return a linked list which contains the non-common elements. I know how to do it in O(n^2), any way to do it in O(n)?
Use a hash table.
Iterate through the first linked list, entering the values you come across into a hash table.
Iterate through the second linked list, adding any element not found into the hash table into your list of non-common elements.
This solution should be O(n), assuming no collisions in the hash table.
create a new empty list. have a hash table and populate it with elements of both lists. complexity n. then iterate over each list sequentially and while iterating, put those elements in the new list which are not present in the hash table. complexity n. overall complexity=n
If they're unsorted, then I don't believe it is possible to get better than O(n^2). However, you can do better by sorting them... you can sort in reasonably fast time, and then get something like O(nlogn) (I'm not certain that's what it would be, but I think it can be that fast if you use the right algorithm).
Is the best way to sort an array in Delphi is "alphanumeric".
I found this comment in an old code of my application
" The elements of this array must be in ascending, alphanumeric
sort order."
If so ,what copuld be the reason?
-Vas
There's no "best" way as to how to sort the elements of an array (or any collection for that fact). Sort is a humanized characteristic (things are not usually sorted) so I'm guessing the comment has more to do with what your program is expecting.
More concretely, there's probably other section of code elsewhere that expect the array elements to be sorted alphanumerically. It can be something so simple as displaying it into a TreeView already ordered so that the calling code doesn't have to sort the array first.
Arrays are represented as a contiguous memory assignment so that access is fast. Internally the compiler just does a call to GetMem asking for SizeOf(Type) * array size. There's nothing in the way the elements are sorted that affects the performance or memory size of the arrays in general. It MUST be in the program logic.
Most often an array is sorted to provide faster search times. Given a list of length L, I can compare with the midpoint (L DIV 2) and quickly determine if I need to look at the greater half, or the lesser half, and recursively continue using this pattern until I either have nothing to divide by or have found my match. This is what is called a Binary search. If the list is NOT sorted, then this type of operation is not available and instead I must inspect every item in the list until I reach the end.
No, there is no "best way" of sorting. And that's one of the reasons why you have multiple sorting techniques out there.
With QuickSort, you even provide the comparison function where you determine what order you ultimately want.
Sorting an array in some way is useful when you're trying to do a binary search on the array. A binary search can be extremely fast, compared to other methods. But if the sort error is wrong, the search will be unable to find the record.
Other reasons to keep arrays sorted are almost always for cosmetic reasons, to decide how the array is sent to some output.
The best way to re-order an array depends of the length of the array and the type of data it contains. A QuickSort algorithm would give a fast result in most cases. Delphi uses it internally when you're working with string-lists and some other lists. Question is, do you really need to sort it? Does it really need to stay an array even?
But the best way to keep an array sorted is by keeping it sorted from the first element that you add to it! In general, I write a wrapper around my array types, which will take care of keeping the array ordered. The 'Add' method will search for the biggest value in the array that's less or equal to the value that I want to add. I then insert the new item right after that position. To me, that would be the best solution. (With big arrays you could use the binary search method again to find the location where you need to insert the new record. It's slower than appending records to the end but you never have to wonder if it's sorted or not, since it is...