Get object by key with certain value from NSDictionary - objective-c

Question

I have NSDictionary with objects. The NSDictionary is consist of json(You can see it below). I need to populate my table view with the name by id. And the id can repeat. It means I can have several "name" with id which is equal 0. I should get name by key with certain value from the dictionary. Here is my NSDictionary:
{
name = "smth1";
id = 0;
},
{
name = "smth2";
id = 1;
},
{
name = "smth3";
id = 2;
},
{
name = "smth4";
id = 2;
},
...
For example, I want to get value of key "name" where id is 2. Then I will get name = "smth3" and name = "smth4". Generally, I am trying to populate my table view component with the nested data. How can I do this? Any tips, ideas. Thank you.

Answer 1

Actually you show an array of dictionaries, where each dictionary has 2 keys.
You could use the NSArray function indexOfObjectPassingTest. That code might look like this (starting from an NSArray) :
int idToFind = 2;
NSArray *dictArray = #[#{#"name": #"smth1",
#"id": #(0)},
#{#"name": #"smth2",
#"id": #(1)},
#{#"name": #"smth3",
#"id": #(2)}
];
NSUInteger dictIndex =
[dictArray indexOfObjectPassingTest: ^BOOL(
NSDictionary *dict,
NSUInteger idx,
BOOL *stop) {
return [dict[#"id"] intValue] == idToFind;
}];
if (dictIndex != NSNotFound) {
NSLog(#"Found id %d with name %#", idToFind, dictArray[dictIndex][#"name"]);
}
}
EDIT:
If you need to match all of the items then you need to use the NSArray method indexesOfObjectsPassingTest. That finds all the items in an array that match.
That code would look like this:
int idToFind = 2;
NSArray *dictArray = #[#{#"name": #"smth1",
#"id": #(0)},
#{#"name": #"Fred",
#"id": #(2)},
#{#"name": #"smth2",
#"id": #(1)},
#{#"name": #"smth3",
#"id": #(2)},
];
NSIndexSet *dictIndexes;
dictIndexes =
[dictArray indexesOfObjectsPassingTest: ^BOOL(NSDictionary *dict,
NSUInteger idx,
BOOL *stop)
{
return [dict[#"id"] intValue] == idToFind;
}];
if (dictIndexes.count == 0) {
NSLog(#"No matches found");
}
[dictIndexes enumerateIndexesUsingBlock:^(NSUInteger index,
BOOL * _Nonnull stop)
{
NSLog(#"Found id=%# with name \"%#\" at index %lu",
dictArray[index][#"id"],
dictArray[index][#"name"],
index);
}];
Both approaches above use methods that take a block. The block contains code that you write that returns a BOOL for the item(s) that match your desired search criteria.
Search/sort methods that take blocks are very flexible because you can provide any code you want to do the matching/comparison.
The indexOfObjectPassingTest method searches for a single object in your array and stops when it finds the first match.
In contrast, the indexesOfObjectsPassingTest function will match multiple items. It returns an NSIndexSet, a special class that's used to index into NSArrays.
There is a function enumerateIndexesUsingBlock that invokes a block of code for each index specified in the array.
We could also have used the method objectsAtIndexes to extract only the elements in the array that are listed in the resulting index set, and then used for...in to loop through the items. That code would look like this:
NSArray *filteredArray = [dictArray objectsAtIndexes: dictIndexes];
for (NSDictionary *aDict in filteredArray) {
NSLog(#"Found id=%# with name \"%#\"", aDict[#"id"], aDict[#"name"]);
}
Note that this sort of thing is simpler and cleaner in Swift. We could use a filter statement on the array and provide a closure that selects items that match our search criteria