I need to search a string in the string array. I dont want to use any for looping in it
string [] arr = {"One","Two","Three"};
string theString = "One"
I need to check whether theString variable is present in arr.
Well, something is going to have to look, and looping is more efficient than recursion (since tail-end recursion isn't fully implemented)... so if you just don't want to loop yourself, then either of:
bool has = arr.Contains(var); // .NET 3.5
or
bool has = Array.IndexOf(arr, var) >= 0;
For info: avoid names like var - this is a keyword in C# 3.0.
Every method, mentioned earlier does looping either internally or externally, so it is not really important how to implement it. Here another example of finding all references of target string
string [] arr = {"One","Two","Three"};
var target = "One";
var results = Array.FindAll(arr, s => s.Equals(target));
Does it have to be a string[] ? A List<String> would give you what you need.
List<String> testing = new List<String>();
testing.Add("One");
testing.Add("Two");
testing.Add("Three");
testing.Add("Mouse");
bool inList = testing.Contains("Mouse");
bool exists = arr.Contains("One");
I think it is better to use Array.Exists than Array.FindAll.
Its pretty simple. I always use this code to search string from a string array
string[] stringArray = { "text1", "text2", "text3", "text4" };
string value = "text3";
int pos = Array.IndexOf(stringArray, value);
if (pos > -1)
{
return true;
}
else
{
return false;
}
If the array is sorted, you can use BinarySearch. This is a O(log n) operation, so it is faster as looping. If you need to apply multiple searches and speed is a concern, you could sort it (or a copy) before using it.
Each class implementing IList has a method Contains(Object value). And so does System.Array.
Why the prohibition "I don't want to use any looping"? That's the most obvious solution. When given the chance to be obvious, take it!
Note that calls like arr.Contains(...) are still going to loop, it just won't be you who has written the loop.
Have you considered an alternate representation that's more amenable to searching?
A good Set implementation would perform well. (HashSet, TreeSet or the local equivalent).
If you can be sure that arr is sorted, you could use binary search (which would need to recurse or loop, but not as often as a straight linear search).
You can use Find method of Array type. From .NET 3.5 and higher.
public static T Find<T>(
T[] array,
Predicate<T> match
)
Here is some examples:
// we search an array of strings for a name containing the letter “a”:
static void Main()
{
string[] names = { "Rodney", "Jack", "Jill" };
string match = Array.Find (names, ContainsA);
Console.WriteLine (match); // Jack
}
static bool ContainsA (string name) { return name.Contains ("a"); }
Here’s the same code shortened with an anonymous method:
string[] names = { "Rodney", "Jack", "Jill" };
string match = Array.Find (names, delegate (string name)
{ return name.Contains ("a"); } ); // Jack
A lambda expression shortens it further:
string[] names = { "Rodney", "Jack", "Jill" };
string match = Array.Find (names, n => n.Contains ("a")); // Jack
At first shot, I could come up with something like this (but it's pseudo code and assuming you cannot use any .NET built-in libaries). Might require a bit of tweaking and re-thinking, but should be good enough for a head-start, maybe?
int findString(String var, String[] stringArray, int currentIndex, int stringMaxIndex)
{
if currentIndex > stringMaxIndex
return (-stringMaxIndex-1);
else if var==arr[currentIndex] //or use any string comparison op or function
return 0;
else
return findString(var, stringArray, currentIndex++, stringMaxIndex) + 1 ;
}
//calling code
int index = findString(var, arr, 0, getMaxIndex(arr));
if index == -1 printOnScreen("Not found");
else printOnScreen("Found on index: " + index);
In C#, if you can use an ArrayList, you can use the Contains method, which returns a boolean:
if MyArrayList.Contains("One")
You can check the element existence by
arr.Any(x => x == "One")
it is old one ,but this is the way i do it ,
enter code herevar result = Array.Find(names, element => element == "One");
I'm surprised that no one suggested using Array.IndexOf Method.
Indeed, Array.IndexOf has two advantages :
It allows searching if an element is included into an array,
It gets at the same time the index into the array.
int stringIndex = Array.IndexOf(arr, theString);
if (stringIndex >= 0)
{
// theString has been found
}
Inline version :
if (Array.IndexOf(arr, theString) >= 0)
{
// theString has been found
}
Using Contains()
string [] SomeArray = {"One","Two","Three"};
bool IsExist = SomeArray.Contains("One");
Console.WriteLine("Is string exist: "+ IsExist);
Using Find()
string [] SomeArray = {"One","Two","Three"};
var result = Array.Find(SomeArray, element => element == "One");
Console.WriteLine("Required string is: "+ result);
Another simple & traditional way, very useful for beginners to build logic.
string [] SomeArray = {"One","Two","Three"};
foreach (string value in SomeArray) {
if (value == "One") {
Console.WriteLine("Required string is: "+ value);
}
}
Related
I only found a way to do it the opposite way round: create a comma separated string from an int list or array, but not on how to convert input like string str = "1,2,3,4,5"; to an array or list of ints.
Here is my implementation (inspired by this post by Eric Lippert):
public static IEnumerable<int> StringToIntList(string str)
{
if (String.IsNullOrEmpty(str))
{
yield break;
}
var chunks = str.Split(',').AsEnumerable();
using (var rator = chunks.GetEnumerator())
{
while (rator.MoveNext())
{
int i = 0;
if (Int32.TryParse(rator.Current, out i))
{
yield return i;
}
else
{
continue;
}
}
}
}
Do you think this is a good approach or is there a more easy, maybe even built in way?
EDIT: Sorry for any confusion, but the method needs to handle invalid input like "1,2,,,3" or "###, 5," etc. by skipping it.
You should use a foreach loop, like this:
public static IEnumerable<int> StringToIntList(string str) {
if (String.IsNullOrEmpty(str))
yield break;
foreach(var s in str.Split(',')) {
int num;
if (int.TryParse(s, out num))
yield return num;
}
}
Note that like your original post, this will ignore numbers that couldn't be parsed.
If you want to throw an exception if a number couldn't be parsed, you can do it much more simply using LINQ:
return (str ?? "").Split(',').Select<string, int>(int.Parse);
If you don't want to have the current error handling behaviour, it's really easy:
return text.Split(',').Select(x => int.Parse(x));
Otherwise, I'd use an extra helper method (as seen this morning!):
public static int? TryParseInt32(string text)
{
int value;
return int.TryParse(text, out value) ? value : (int?) null;
}
and:
return text.Split(',').Select<string, int?>(TryParseInt32)
.Where(x => x.HasValue)
.Select(x => x.Value);
or if you don't want to use the method group conversion:
return text.Split(',').Select(t => t.TryParseInt32(t)
.Where(x => x.HasValue)
.Select(x => x.Value);
or in query expression form:
return from t in text.Split(',')
select TryParseInt32(t) into x
where x.HasValue
select x.Value;
Without using a lambda function and for valid inputs only, I think it's clearer to do this:
Array.ConvertAll<string, int>(value.Split(','), Convert.ToInt32);
--EDIT-- It looks like I took his question heading too literally - he was asking for an array of ints rather than a List --EDIT ENDS--
Yet another helper method...
private static int[] StringToIntArray(string myNumbers)
{
List<int> myIntegers = new List<int>();
Array.ForEach(myNumbers.Split(",".ToCharArray()), s =>
{
int currentInt;
if (Int32.TryParse(s, out currentInt))
myIntegers.Add(currentInt);
});
return myIntegers.ToArray();
}
quick test code for it, too...
static void Main(string[] args)
{
string myNumbers = "1,2,3,4,5";
int[] myArray = StringToIntArray(myNumbers);
Console.WriteLine(myArray.Sum().ToString()); // sum is 15.
myNumbers = "1,2,3,4,5,6,bad";
myArray = StringToIntArray(myNumbers);
Console.WriteLine(myArray.Sum().ToString()); // sum is 21
Console.ReadLine();
}
Let us assume that you will be reading the string from the console. Import System.Linq and try this one:
int[] input = Console.ReadLine()
.Split(',', StringSplitOptions.RemoveEmptyEntries)
.Select(int.Parse)
.ToArray();
This has been asked before. .Net has a built-in ConvertAll function for converting between an array of one type to an array of another type. You can combine this with Split to separate the string to an array of strings
Example function:
static int[] ToIntArray(this string value, char separator)
{
return Array.ConvertAll(value.Split(separator), s=>int.Parse(s));
}
Taken from here
This is for longs, but you can modify it easily to work with ints.
private static long[] ConvertStringArrayToLongArray(string str)
{
return str.Split(",".ToCharArray()).Select(x => long.Parse(x.ToString())).ToArray();
}
I don't see why taking out the enumerator explicitly offers you any advantage over using a foreach. There's also no need to call AsEnumerable on chunks.
import java.util.*;
import java.io.*;
public class problem
{
public static void main(String args[])enter code here
{
String line;
String[] lineVector;
int n,m,i,j;
Scanner sc = new Scanner(System.in);
line = sc.nextLine();
lineVector = line.split(",");
//enter the size of the array
n=Integer.parseInt(lineVector[0]);
m=Integer.parseInt(lineVector[1]);
int arr[][]= new int[n][m];
//enter the array here
System.out.println("Enter the array:");
for(i=0;i<n;i++)
{
line = sc.nextLine();
lineVector = line.split(",");
for(j=0;j<m;j++)
{
arr[i][j] = Integer.parseInt(lineVector[j]);
}
}
sc.close();
}
}
On the first line enter the size of the array separated by a comma. Then enter the values in the array separated by a comma.The result is stored in the array arr.
e.g
input:
2,3
1,2,3
2,4,6
will store values as
arr = {{1,2,3},{2,4,6}};
I'm a student and I was wondering what the most efficient way is to check if a certain value is present in a array.
My second attempt:
string value = "pow";
string[] array = new string[] { "pong", "ping", "pow" };
bool valueIsInArray = false;
foreach(var s in array) if (s == value) valueIsInArray = true;
if (valueIsInArray)
{
// code here
}
I've researched and found if I were to use LINQ the code would look like this:
string value = "oink"; // value given to the method
string[] array = new string[] { "oink", "oink", "baboinkadoink" };
if (array.Contains(value))
{
//code here
}
The question is if using LINQ in anyway negatively impacts the speed or consistency of the code, and if there is an even better way to go about doing this?
Use linq Any(), The enumeration of source is stopped as soon as the result can be determined.
string value = "pow";
string[] array = new string[] { "pong", "ping", "pow" };
bool isValuePresent = array.Any(x => x == value);
https://msdn.microsoft.com/en-us/library/bb534972(v=vs.110).aspx
As a commenter said, LiNQ won't really trouble you here. The difference is microscopic (even on larger collections). However, if you must use an alternative, use IndexOf. See: https://msdn.microsoft.com/en-us/library/system.array.indexof(v=vs.110).aspx
Example:
string value = "oink"; // value given to the method
string[] array = new string[] { "oink", "oink", "baboinkadoink" };
if (Array.IndexOf(array, value) > -1)
{
//code here
}
Although I'm not sure what Contains ends up doing underwater, but they probably make a call to IndexOf aswell.
Willy-nilly you have to scan the array up to the first match (or entire array if there's no match); you can either put foreach loop:
bool valueIsInArray = false;
foreach (var item in array)
if (item == value) {
valueIsInArray = true;
break;
}
use for one:
bool valueIsInArray = false;
foreach (int i = 0; i < array.Length; ++i)
if (array[i] == value) {
valueIsInArray = true;
break;
}
Try Array class:
bool valueIsInArray = array.Contains(value);
Implement the code with a help of Linq:
bool valueIsInArray = array.Any(item => item == value);
The difference of these methods is a question of microseconds (if any); that's why put the version which is the most readable for you. My own choice is array.Contains(value) - let the system work for you and hide unwanted details (e.g. break in the loop)
You shoud have to iterate through the entire array for checking the value.
Either Linq or Conventional looping methods. Or you can use the
Array.Find()
also for the same. Better to go with the Linq and make the code is more simpler.
Happy coding
I saw this question that asks given a string "smith;rodgers;McCalne" how can you produce a collection. The answer to this was to use String.Split.
If we don't have Split() built in what do you do instead?
Update:
I admit writing a split function is fairly easy. Below is what I would've wrote. Loop through the string using IndexOf and extract using Substring.
string s = "smith;rodgers;McCalne";
string seperator = ";";
int currentPosition = 0;
int lastPosition = 0;
List<string> values = new List<string>();
do
{
currentPosition = s.IndexOf(seperator, currentPosition + 1);
if (currentPosition == -1)
currentPosition = s.Length;
values.Add(s.Substring(lastPosition, currentPosition - lastPosition));
lastPosition = currentPosition+1;
} while (currentPosition < s.Length);
I took a peek at SSCLI implementation and its similar to the above except it handles way more use cases and it uses an unsafe method to determine the indexes of the separators before doing the substring extraction.
Others have suggested the following.
An Extension Method that uses an Iterator Block
Regex suggestion (no implementation)
Linq Aggregate method
Is this it?
It's reasonably simple to write your own Split equivalent.
Here's a quick example, although in reality you'd probably want to create some overloads for more flexibility. (Well, in reality you'd just use the framework's built-in Split methods!)
string foo = "smith;rodgers;McCalne";
foreach (string bar in foo.Split2(";"))
{
Console.WriteLine(bar);
}
// ...
public static class StringExtensions
{
public static IEnumerable<string> Split2(this string source, string delim)
{
// argument null checking etc omitted for brevity
int oldIndex = 0, newIndex;
while ((newIndex = source.IndexOf(delim, oldIndex)) != -1)
{
yield return source.Substring(oldIndex, newIndex - oldIndex);
oldIndex = newIndex + delim.Length;
}
yield return source.Substring(oldIndex);
}
}
You make your own loop to do the split. Here is one that uses the Aggregate extension method. Not very efficient, as it uses the += operator on the strings, so it should not really be used as anything but an example, but it works:
string names = "smith;rodgers;McCalne";
List<string> split = names.Aggregate(new string[] { string.Empty }.ToList(), (s, c) => {
if (c == ';') s.Add(string.Empty); else s[s.Count - 1] += c;
return s;
});
Regex?
Or just Substring. This is what Split does internally
If I have an array of ints, and I want to quickly check if a certain int value is in that array, is there a method to do that?
If the array is sorted, then this is quickest:
Array.BinarySearch(myArray, value) >= 0;
If the array is searched a lot and rarely modified, then you may find it worthwhile to sort the array after modification (using Array.Sort) and use the above. Otherwise, use the option you prefer:
Array.IndexOf(myArray, value) >= 0; //.Net 1
Array.Exists(array, delegate(int x) { return x == value; }); //.Net 2
myArray.Contains(value); //.Net 3
IndexOf has the best performance for unsorted arrays. The second option uses a predicate delegate, and the third requires the creation of an enumerator object.
Use for example this, if you want to check if your array contains the int 0:
if (your_int_array.Contains(0))
{
//Code
}
The Enumerable.Contains() Method is your friend in .NET-Framework 3.5...
Enumerable.Contains if you're using C# 3.0 or later.
e.g.
var contained = myArray.Contains(4);
You could use the IndexOf method:
int[] array = new int[] { 1, 2, 3 };
bool isArrayContains17 = Array.IndexOf(array, 17) > -1;
var myArray = new [] { 1, 2};
if myArray.Contains(1)
{
do something
}
You may need a using System.Linq;
Kindness,
Dan
Try this function:
public static bool FindValueFromArray(object[] Values,object valueToSearch){
bool retVal = false;
Array myArray = (Array)Values;
int found = Array.BinarySearch(myArray, valueToSearch);
if (found != -1){
retVal = true;
}
return retVal;
}
Hope this helps.
I only found a way to do it the opposite way round: create a comma separated string from an int list or array, but not on how to convert input like string str = "1,2,3,4,5"; to an array or list of ints.
Here is my implementation (inspired by this post by Eric Lippert):
public static IEnumerable<int> StringToIntList(string str)
{
if (String.IsNullOrEmpty(str))
{
yield break;
}
var chunks = str.Split(',').AsEnumerable();
using (var rator = chunks.GetEnumerator())
{
while (rator.MoveNext())
{
int i = 0;
if (Int32.TryParse(rator.Current, out i))
{
yield return i;
}
else
{
continue;
}
}
}
}
Do you think this is a good approach or is there a more easy, maybe even built in way?
EDIT: Sorry for any confusion, but the method needs to handle invalid input like "1,2,,,3" or "###, 5," etc. by skipping it.
You should use a foreach loop, like this:
public static IEnumerable<int> StringToIntList(string str) {
if (String.IsNullOrEmpty(str))
yield break;
foreach(var s in str.Split(',')) {
int num;
if (int.TryParse(s, out num))
yield return num;
}
}
Note that like your original post, this will ignore numbers that couldn't be parsed.
If you want to throw an exception if a number couldn't be parsed, you can do it much more simply using LINQ:
return (str ?? "").Split(',').Select<string, int>(int.Parse);
If you don't want to have the current error handling behaviour, it's really easy:
return text.Split(',').Select(x => int.Parse(x));
Otherwise, I'd use an extra helper method (as seen this morning!):
public static int? TryParseInt32(string text)
{
int value;
return int.TryParse(text, out value) ? value : (int?) null;
}
and:
return text.Split(',').Select<string, int?>(TryParseInt32)
.Where(x => x.HasValue)
.Select(x => x.Value);
or if you don't want to use the method group conversion:
return text.Split(',').Select(t => t.TryParseInt32(t)
.Where(x => x.HasValue)
.Select(x => x.Value);
or in query expression form:
return from t in text.Split(',')
select TryParseInt32(t) into x
where x.HasValue
select x.Value;
Without using a lambda function and for valid inputs only, I think it's clearer to do this:
Array.ConvertAll<string, int>(value.Split(','), Convert.ToInt32);
--EDIT-- It looks like I took his question heading too literally - he was asking for an array of ints rather than a List --EDIT ENDS--
Yet another helper method...
private static int[] StringToIntArray(string myNumbers)
{
List<int> myIntegers = new List<int>();
Array.ForEach(myNumbers.Split(",".ToCharArray()), s =>
{
int currentInt;
if (Int32.TryParse(s, out currentInt))
myIntegers.Add(currentInt);
});
return myIntegers.ToArray();
}
quick test code for it, too...
static void Main(string[] args)
{
string myNumbers = "1,2,3,4,5";
int[] myArray = StringToIntArray(myNumbers);
Console.WriteLine(myArray.Sum().ToString()); // sum is 15.
myNumbers = "1,2,3,4,5,6,bad";
myArray = StringToIntArray(myNumbers);
Console.WriteLine(myArray.Sum().ToString()); // sum is 21
Console.ReadLine();
}
Let us assume that you will be reading the string from the console. Import System.Linq and try this one:
int[] input = Console.ReadLine()
.Split(',', StringSplitOptions.RemoveEmptyEntries)
.Select(int.Parse)
.ToArray();
This has been asked before. .Net has a built-in ConvertAll function for converting between an array of one type to an array of another type. You can combine this with Split to separate the string to an array of strings
Example function:
static int[] ToIntArray(this string value, char separator)
{
return Array.ConvertAll(value.Split(separator), s=>int.Parse(s));
}
Taken from here
This is for longs, but you can modify it easily to work with ints.
private static long[] ConvertStringArrayToLongArray(string str)
{
return str.Split(",".ToCharArray()).Select(x => long.Parse(x.ToString())).ToArray();
}
I don't see why taking out the enumerator explicitly offers you any advantage over using a foreach. There's also no need to call AsEnumerable on chunks.
import java.util.*;
import java.io.*;
public class problem
{
public static void main(String args[])enter code here
{
String line;
String[] lineVector;
int n,m,i,j;
Scanner sc = new Scanner(System.in);
line = sc.nextLine();
lineVector = line.split(",");
//enter the size of the array
n=Integer.parseInt(lineVector[0]);
m=Integer.parseInt(lineVector[1]);
int arr[][]= new int[n][m];
//enter the array here
System.out.println("Enter the array:");
for(i=0;i<n;i++)
{
line = sc.nextLine();
lineVector = line.split(",");
for(j=0;j<m;j++)
{
arr[i][j] = Integer.parseInt(lineVector[j]);
}
}
sc.close();
}
}
On the first line enter the size of the array separated by a comma. Then enter the values in the array separated by a comma.The result is stored in the array arr.
e.g
input:
2,3
1,2,3
2,4,6
will store values as
arr = {{1,2,3},{2,4,6}};