Question

NSMutableDictionary *expense_ArrContents = [[NSMutableDictionary alloc]init];
for (int i = 1; i<=4; i++) {
    NSMutableArray *current_row = [NSMutableArray arrayWithObjects:@"payer_id",@"Expense_Type_id",@"Category_Id",@"SubCategory_Id",nil];
    [expense_ArrContents setObject:current_row forKey: [NSNumber numberWithInt:i]];
}
NSArray *newArray = [expense_ArrContents allKeysForObject:@"payer_id"];
NSLog(@"%@",[newArray description]);

i want to get the list of key values containing the particular object which is in the array of values stored in nsmutabledictionary for a particular key.

Answer 1

In the line where you get all the keys ([expense_ArrContents allKeysForObject:@"payer_id"];) you actually get keys for an object that is not in any of the array’s items. This @"player_id" is different object than the @"player_id" you added in current_row. In fact, maybe all of your rows have different @"player_id" objects (except if the compiler has made some optimization – maybe it threats that same string literal as one object instead of creating new object for each iteration).
Try creating an NSString object for the @"player_id" which you add to the current_row and then get all the keys for that same object:

NSString* playerId = @"player_id";
for(){
    NSMutableArray *current_row = [NSMutableArray arrayWithObjects: playerId,...];
...
}
NSArray *newArray = [expense_ArrContents allKeysForObject:playerId];