I have a mutable array of strings. For this example, let's say there are 2 strings in it.
The operation that I would like to do is take the first string and assign the value of the second string to it.
I was trying something like this:
- (void) someAction {
NSMutableArray * array = [[NSMutableArray alloc] initWithObjects: string1, string2, nil];
NSString * firstString = [array objectAtIndex:0];
NSString * secondString = [array objectAtIndex:1];
firstString = secondString;
}
But this method doesn't seem to work. As after I log these two strings, they don't change after the operation.
Please advise.
You can't change strings in an array like that.
The array contains pointers to the strings, and when you assign one string to another you are just swapping pointers around, not changing the string object that the array points to.
What you need to do to swap the string in the array is this:
- (void) someAction {
NSMutableArray * array = [[NSMutableArray alloc] initWithObjects: string1, string2, nil];
NSString * secondString = [array objectAtIndex:1];
[array replaceObjectAtIndex:0 withObject:secondString]; //replace first string with second string in the array
}
Related
I have an NSArray, where each object contains a specific class called Card. Card has a description method. I want to join all objects in the array using the output of the description method, separated by spaces. Is there a simple to do this, without manually iterating the NSArray and manipulating NSString?
Something akin to the following made-up code?
NSArray *myArray = getCards(); // fetches 10 items or more
NSString *myString = [myArray joinUsingDescriptionMethodSeparatedBy:#" "];
or
NSString *myString = [NSString stringFromArrayDescriptionMethods:myArray separatedBy:#" "];
Naturally ,I could implement this myself but I suspect there could be something already present that does this.
I don't think that there is such a method. You can also implement it in a Category for NSString.
Sorry, I found this:
NSString * result = [[array valueForKey:#"description"] componentsJoinedByString:#""];
From the documentation:
Constructs and returns an NSString object that is the result of
interposing a given separator between the elements of the array.
- (NSString *)componentsJoinedByString:(NSString *)separator
Do this for description method of each NSArray item:
NSMutableString * result = [[NSMutableString alloc] init];
for (NSObject * obj in array)
{
[result appendString:[NSString stringWithFormat:#" %#"[obj description]]];
}
NSLog(#"The concatenated string is %#", result);
i'm new to obj-c (this is my first day class eheh) and i'm trying to change a label with a random string from a multidimensional array. plus, every time the button is hitten you switch the array. i know it's a bit odd eheh… this is the IBAction:
UIButton *button = (UIButton *)sender;
NSMutableArray *firstArray = [NSMutableArray array];
[firstArray addObject:#"foo"];
NSMutableArray *secondArray = [NSMutableArray array];
[secondArray addObject:#"bar"];
NSMutableArray *frasi = [NSMutableArray array];
[frasi addObject:firstArray];
[frasi addObject:secondArray];
NSMutableArray *array = [NSMutableArray arrayWithObjects:[frasi objectAtIndex:[button isSelected]], nil];
NSString *q = [array objectAtIndex: (arc4random()% [array count] )];
NSString *lab = [NSString stringWithFormat:#"%#", q];
self.label.text = lab;
all works, but the new label is
( "foo" )
instead of just foo (without quotes)... probably i mess in the last block of code...
ty
So, you create 2 mutable arrays, then add them to a new mutable array frasi. Then you get one of those two arrays and use it as the single element (because you use arrayWithObjects: instead of arrayWithArray:) of a new array array.
So array is an array that contains a single array element (instead of an array of strings as you may believe).
When you get an object from array, it's always the same single object that was used to initialize it: either firstArray or secondArray.
So you get an array of strings where you expect a string. When using stringWithFormat:, the specifier %# is replaced with the string description of that object.
A string returns itself as its own description. But the description of an array is the list of all its elements separated with commas and surrounded by parenthesis, which is why you get ( "foo" ).
So instead or creating unneeded arrays, you may just replace all the 8th last lines with this:
NSArray *array = [button isSelected] ? secondArray : firstArray;
self.label.text = [array objectAtIndex:arc4_uniform([array count])];
Actually u have array within array
Replace this line with yours:
NSString *q = [[array objectAtIndex: (arc4random()% [array count] )] objectAtIndex:0];
I have a NSMutableArray and I need to sort its elements into separate C char.
How to accomplish that? Or is it better to put the elements into NSStrings?
I've tried this, and it crashes when I try to log the result:
NSMutableArray *array = [[NSMutableArray alloc] init];
... do something to fill the array ...
NSString *string;
string = [array objectAtIndex:0];
NSLog(#"String: %#", string);
*I really prefer putting the elements of the array into C char, because I already have some woking code using char instead of NSStrin*g.
Thanks!
Dont see any specific reason to convert NSString to C chars. To sort an array full of NSStrings try this method -
NSMutableArray *array = [[NSMutableArray alloc] init];
sortedArray = [array sortedArrayUsingSelector:#selector(localizedCaseInsensitiveCompare:)];
NSString *string = [sortedArray objectAtIndex:0];
NSLog(#"String: %#", string);
Does NSArray have the capability of matching a string in an array with the closest representation of that string in another array?
For example:
NSString *search = #"apple p";
NSArray *array = [[NSArray alloc]initWithObjects:#"apple",#"apple pie",#"apple pies", #"apple juice", nil];
//Now we want to look for a similar string
[array ?];
The desired result should be: apple pie (most similar string). Any ideas how this could be done?
You could sort the array based on similarity, then retrieve the last element in the sorted array: the most similar string. Assuming you've defined some method similarityTo: in a category on NSString, something like the following should do the trick:
NSInteger compareStrings(id a, id b, void *context) {
int aSimilarity = [a similarityTo:(NSString *)context];
int bSimilarity = [b similarityTo:(NSString *)context];
return aSimilarity - bSimilarity;
}
// Retrieving the most similar string.
NSString *result = [[array sortedArrayUsingFunction:compareStrings
context:search] lastObject];
is it an possible to add a value from an NSMutableString into an NSArray? Whats the snippet?
Actually, Mike is wrong. If you want to instantiate an NSArray with a single NSMutableString object, you can do the following:
NSMutableString *myString; //Assuming your string is here
NSArray *array = [NSArray arrayWithObject:myString];
There is no arrayWithElements in NSArray (see NSArray documentation)
If you want to instantiate an NSArray with a single NSMutableString object, you can do the following:
NSString *myString; //Assuming your string is here
NSArray *array = [NSArray arrayWithObjects:myString,nil];
Note that NSArray will be immutable - that is, you can't add or remove objects to it after you've made it. If you want the array to be mutable, you'll have to create an NSMutableArray. To use an NSMutableArray in this fashion, you can do the following:
NSString *myString; //Assuming your string is here
NSMutableArray *array = [[NSMutableArray alloc] init];
[array addObject:myString];
NSArray is immutable, so you cannot add values to it. You should use NSMutableArray in order to do that with the addObject: method.
NSMutableString *str = ...
NSMutableArray *array = [[NSMutableArray alloc] init];
[array addObject:str];
// You must use NSMutableArray to add Object to array
NSMutableArray *tableCellNames;
// arrayWithCapacity is a required parameter to define limit of your object.
tableCellNames = [NSMutableArray arrayWithCapacity:total_rows];
[tableCellNames addObject:title];
NSLog(#"Array table cell %#",tableCellNames);
//Thanks VKJ
An elegant solution would be this:
NSMutableString *str; //your string here
NSArray *newArray = #[str];
Using the new notation, it's a piece of cake.