I have a large list and I would like to overwrite one value if required. To do this, I create two subsets of the list which seems to give me an OutOfMemoryException. Here is my code snippet:
if (ownRG != "")
{
List<string> maclist = ownRG.Split(',').ToList();
List<IVFile> temp = powlist.Where(a => maclist.Contains(a.Machine)).ToList();
powlist = powlist.Where(a => !maclist.Contains(a.Machine)).ToList(); // OOME Here
temp.ForEach(a => { a.ReportingGroup = ownRG; });
powlist.AddRange(temp);
}
Essentially I'm splitting the list into the part that needs updating and the part that doesn't, then I perform the update and put the list back together. This works fine for smaller lists, but breaks with an OutOfMemoryException on the third row within the if for a large list. Can I make this more efficient?
NOTE
powlist is the large list (>1m) items. maclist only has between 1 and 10 but even with 1 item this breaks.
Solving your issue
Here is how to rearrange your code using the enumerator code from my answer:
if (!string.IsNullOrEmpty(ownRG))
{
var maclist = new CommaSeparatedStringEnumerable(str);
var temp = powlist.Where(a => maclist.Contains(a.Machine));
foreach (var p in temp)
{
p.ReportingGroup = ownRG;
}
}
You should not use ToList in your code.
You don't need to remove thee contents of temp from powlist (you are re-adding them anyway)
Streaming over a large comma-separated string
You can iterate over the list manually instead of doing what you do now, by looking for , characters and remembering the position of the last found one and the one before. This will definitely make your app work because then it won't need to store the entire set in the memory at once.
Code example:
var str = "aaa,bbb,ccc";
var previousComma = -1;
var currentComma = 0;
for (; (currentComma = str.IndexOf(',', previousComma + 1)) != -1; previousComma = currentComma)
{
var currentItem = str.Substring(previousComma + 1, currentComma - previousComma - 1);
Console.WriteLine(currentItem);
}
var lastItem = str.Substring(previousComma + 1);
Console.WriteLine(lastItem);
Custom iterator
If you want to do it 'properly' in a fancy way, you can even write a custom enumerator:
public class CommaSeparatedStringEnumerator : IEnumerator<string>
{
int previousComma = -1;
int currentComma = -1;
string bigString = null;
bool atEnd = false;
public CommaSeparatedStringEnumerator(string s)
{
if (s == null)
throw new ArgumentNullException("s");
bigString = s;
this.Reset();
}
public string Current { get; private set; }
public void Dispose() { /* No need to do anything here */ }
object IEnumerator.Current { get { return this.Current; } }
public bool MoveNext()
{
if (atEnd)
return false;
atEnd = (currentComma = bigString.IndexOf(',', previousComma + 1)) == -1;
if (!atEnd)
Current = bigString.Substring(previousComma + 1, currentComma - previousComma - 1);
else
Current = bigString.Substring(previousComma + 1);
previousComma = currentComma;
return true;
}
public void Reset()
{
previousComma = -1;
currentComma = -1;
atEnd = false;
this.Current = null;
}
}
public class CommaSeparatedStringEnumerable : IEnumerable<string>
{
string bigString = null;
public CommaSeparatedStringEnumerable(string s)
{
if (s == null)
throw new ArgumentNullException("s");
bigString = s;
}
public IEnumerator<string> GetEnumerator()
{
return new CommaSeparatedStringEnumerator(bigString);
}
IEnumerator IEnumerable.GetEnumerator()
{
return this.GetEnumerator();
}
}
Then you can iterate over it like this:
var str = "aaa,bbb,ccc";
var enumerable = new CommaSeparatedStringEnumerable(str);
foreach (var item in enumerable)
{
Console.WriteLine(item);
}
Other thoughts
Can I make this more efficient?
Yes, you can. I suggest to either work with a more efficient data format (you can take a look around databases or XML, JSON, etc. depending on your needs). If you really want to work with comma-separated items, see my code examples above.
There's no need to create a bunch of sub-lists from powlist and reconstruct it. Simply loop over the powlist and update the ReportingGroup property accordingly.
var maclist = new HashSet<string>( ownRG.Split(',') );
foreach( var item in powlist) {
if( maclist.Contains( item.Machine ) ){
item.ReportingGroup = ownRG;
}
}
Since this changes powlist in place, you won't allocate any extra memory and shouldn't run into an OutOfMemoryException.
In a loop find the next ',' char. Take the substring between the ',' and the previous ',' position. At the end of the loop save a reference to the previous ',' position (which is initially set to 0). So you parse the items one-by-one rather than all at once.
You can try looping the items of your lists, but this will increase processing time.
foreach(var item in powlist)
{
//do your opeartions
}
Well, first of all, I am not sure whether my title in this question delivered what I want to ask or not. I just do not sure how to describe my problem in one sentence, hopefully the title would not cause any misleading.
If I have a list. Inside the list contain 100 data : list<100>
If I put this list inside a 1 second timer tick and do like this:
myList.RemoveRange(0, 2);
This mean, every 1 second, the data length inside the list will be -2;
This mean, every 1 second, it will be <98> , <96> , <94> .... <0>
Now my problem is...I still have a list, but the list will contain an array: list<array[100]>
Now, what I want is, every 1 second, the data length inside the array inside the list will be -2. But I am not sure know how to do this...
what I want is, every 1 second <array[98]> , <array[96]> , <array[96]> ... <array[0]>
And so, if the list contain <array0[100] , array1[100], array2[100]>
if i put this list inside a loop, every 1 second, it should be
array0[98] , array0[96] ... array0[0]
array1[98] , array1[96] ... array1[0]
array2[98] , array2[96] ... array2[0]
Update:
List<int[]> myList = new List<int[]>();
object myLock = new object();
Random rand = new Random();
public Form1()
{
timer1second.Start();
}
private void SomeMethod()
{
int[] myData = new int [100]
for (int i = 0; i < 100; i++)
{
//generate some random number to store inside myData[]
myData[i] = rand.Next(1 , 10);
}
lock (myLock)
{
myList.Add(myData); //mean List[0] = myData[100]
}
}
private void timer1second_Tick(object sender, EventArgs e)
{
lock (myLock)
{
//do something here in myList to get the myData[100 - 2]
//so that every 1 second tick, the data length inside the MyData will be -2
}
}
Convert the Array item into a List.
Then remove the range from the List
Convert it back to an Array.
Insert it back into the List
Here is a sample:
int currentIndex = 0;
var myList = new List<int[]>();
var intArray = new int[100];
myList.Add(intArray);
// Convert to List.
var newIntArrayList = myList[currentIndex].ToList();
// Remove the ranges
// Index would be based on you logic
newIntArrayList.RemoveRange(0, 2);
//Replace the list with the new arry
myList[currentIndex] = newIntArrayList.ToArray();
Update : Array.Resize should also help.
int currentIndex = 0;
int arrayLength = 100;
var myList = new List<int[]>();
var intArray = new int[100];
myList.Add(intArray);
// Get the array
var array = myList[currentIndex];
// Resize
Array.Resize(ref array, arrayLength-2);
//Replace the list with the update array
myList[currentIndex] = array;
List<int> myList = new List<int>();
for (int i = 1; i < 101; i++)
{
myList.Add(i);
}
for (int i = 100; i > 0; i--)
{
System.Threading.Threading.Sleep(1000);
myList.RemoveAt(i);
i -= 1;
myList.RemoveAt(i);
}
Resizing lists and arrays is an expensive operation. Would you consider a custom data structure for your needs with convinient interface and optimized underlying structure? So every tick you will only increment and integer value representing offset:
class Data
{
const int Step = 2;
List<int[]> data;
List<int> cursors;
public Data()
{
data = new List<int[]>();
}
public void AddArray(int[] array)
{
data.Add(array);
cursors.Add(array.Length);
// or cursors.Add(0), depending on your needs
}
public void Tick()
{
for (int i = 0; i < cursors.Count; i++)
{
cursors[i] -= Step;
// or cursors[i] += Step, depending on your needs
}
}
public IEnumerable<int> GetValuesAtIndex(int index)
{
for (int i = 0, i < data[index].Length; i++)
{
if (i > cursors[index]) // or i < cursors[index]
{
yield return data[index][i];
}
}
}
}
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Array of an unknown length in C#
I want to create a program where users can input there items and those items will be stored in an array. When the user is okay with the amount of items, the program will ask for every item if he got it.
The problem is i cant seem to create an array that is of unknown size. I tried to use something like this: String[] list = new string[]{}; But when the program goes there it gives an IndexOutOfRangeException.
Is there a way i can do this?
This is the full code:
bool groceryListCheck = true;
String[] list = new string[]{};
String item = null;
String yon = null;
int itemscount = 0;
int count = 0;
while (groceryListCheck)
{
Console.WriteLine("What item do you wanna go shop for?");
item = Console.ReadLine();
list[count] = item;
count++;
Console.WriteLine("Done?");
yon = Console.ReadLine();
if (yon == "y")
{
groceryListCheck = false;
itemscount = list.Count();
}
else
{
groceryListCheck = true;
}
}
for (int x = 0; x < itemscount; x++)
{
Console.WriteLine("Did you got the " + list[x] + "?");
Console.ReadKey();
}
Use a List instead of an array.
List<string> myList = new List<string>();
myList.Add("my list item");
After you have gathered all of the items, you can then use a foreach loop to iterate through all of the items in the collection.
foreach(string listItem in myList)
{
Console.WriteLine(listItem);
}
A List<string> would be much easier and more flexible.
There are lots of examples of using a List here which show you a variety of methods to extract data from them.
You can use a List<string> and then, if you need an array as result, you can call the .ToArray() method.
I found that making variable list into a List worked. For instance:
bool groceryListCheck = true;
List<string> list = new List<string>();
String item = null;
String yon = null;
int itemscount = 0;
while (groceryListCheck)
{
Console.WriteLine("What item do you wanna go shop for?");
item = Console.ReadLine();
list.Add(item);
Console.WriteLine("Done?");
yon = Console.ReadLine();
if (yon == "y")
{
groceryListCheck = false;
itemscount = list.Count();
}
else
{
groceryListCheck = true;
}
}
for (int x = 0; x < itemscount; x++)
{
Console.WriteLine("Did you got the " + list[x] + "?");
Console.ReadKey();
}
That is the full code and it works for me.
I would say for this purpose you should use a Hashtable. You can add to it as much as you want and you do not need to specify the size when you create it. Kind of like a really simple database.
See: http://www.dotnetperls.com/hashtable
Probably a really simple one this - I'm starting out with C# and need to add values to an array, for example:
int[] terms;
for(int runs = 0; runs < 400; runs++)
{
terms[] = runs;
}
For those who have used PHP, here's what I'm trying to do in C#:
$arr = array();
for ($i = 0; $i < 10; $i++) {
$arr[] = $i;
}
You can do this way -
int[] terms = new int[400];
for (int runs = 0; runs < 400; runs++)
{
terms[runs] = value;
}
Alternatively, you can use Lists - the advantage with lists being, you don't need to know the array size when instantiating the list.
List<int> termsList = new List<int>();
for (int runs = 0; runs < 400; runs++)
{
termsList.Add(value);
}
// You can convert it back to an array if you would like to
int[] terms = termsList.ToArray();
Edit: a) for loops on List<T> are a bit more than 2 times cheaper than foreach loops on List<T>, b) Looping on array is around 2 times cheaper than looping on List<T>, c) looping on array using for is 5 times cheaper than looping on List<T> using foreach (which most of us do).
Using Linq's method Concat makes this simple
int[] array = new int[] { 3, 4 };
array = array.Concat(new int[] { 2 }).ToArray();
result
3,4,2
If you're writing in C# 3, you can do it with a one-liner:
int[] terms = Enumerable.Range(0, 400).ToArray();
This code snippet assumes that you have a using directive for System.Linq at the top of your file.
On the other hand, if you're looking for something that can be dynamically resized, as it appears is the case for PHP (I've never actually learned it), then you may want to use a List instead of an int[]. Here's what that code would look like:
List<int> terms = Enumerable.Range(0, 400).ToList();
Note, however, that you cannot simply add a 401st element by setting terms[400] to a value. You'd instead need to call Add() like this:
terms.Add(1337);
By 2019 you can use Append, Prepend using LinQ in just one line
using System.Linq;
and then in NET 6.0:
terms = terms.Append(21);
or versions lower than NET 6.0
terms = terms.Append(21).ToArray();
Answers on how to do it using an array are provided here.
However, C# has a very handy thing called System.Collections
Collections are fancy alternatives to using an array, though many of them use an array internally.
For example, C# has a collection called List that functions very similar to the PHP array.
using System.Collections.Generic;
// Create a List, and it can only contain integers.
List<int> list = new List<int>();
for (int i = 0; i < 400; i++)
{
list.Add(i);
}
Using a List as an intermediary is the easiest way, as others have described, but since your input is an array and you don't just want to keep the data in a List, I presume you might be concerned about performance.
The most efficient method is likely allocating a new array and then using Array.Copy or Array.CopyTo. This is not hard if you just want to add an item to the end of the list:
public static T[] Add<T>(this T[] target, T item)
{
if (target == null)
{
//TODO: Return null or throw ArgumentNullException;
}
T[] result = new T[target.Length + 1];
target.CopyTo(result, 0);
result[target.Length] = item;
return result;
}
I can also post code for an Insert extension method that takes a destination index as input, if desired. It's a little more complicated and uses the static method Array.Copy 1-2 times.
Based on the answer of Thracx (I don't have enough points to answer):
public static T[] Add<T>(this T[] target, params T[] items)
{
// Validate the parameters
if (target == null) {
target = new T[] { };
}
if (items== null) {
items = new T[] { };
}
// Join the arrays
T[] result = new T[target.Length + items.Length];
target.CopyTo(result, 0);
items.CopyTo(result, target.Length);
return result;
}
This allows to add more than just one item to the array, or just pass an array as a parameter to join two arrays.
You have to allocate the array first:
int [] terms = new int[400]; // allocate an array of 400 ints
for(int runs = 0; runs < terms.Length; runs++) // Use Length property rather than the 400 magic number again
{
terms[runs] = value;
}
int ArraySize = 400;
int[] terms = new int[ArraySize];
for(int runs = 0; runs < ArraySize; runs++)
{
terms[runs] = runs;
}
That would be how I'd code it.
C# arrays are fixed length and always indexed. Go with Motti's solution:
int [] terms = new int[400];
for(int runs = 0; runs < 400; runs++)
{
terms[runs] = value;
}
Note that this array is a dense array, a contiguous block of 400 bytes where you can drop things. If you want a dynamically sized array, use a List<int>.
List<int> terms = new List<int>();
for(int runs = 0; runs < 400; runs ++)
{
terms.Add(runs);
}
Neither int[] nor List<int> is an associative array -- that would be a Dictionary<> in C#. Both arrays and lists are dense.
You can't just add an element to an array easily. You can set the element at a given position as fallen888 outlined, but I recommend to use a List<int> or a Collection<int> instead, and use ToArray() if you need it converted into an array.
If you really need an array the following is probly the simplest:
using System.Collections.Generic;
// Create a List, and it can only contain integers.
List<int> list = new List<int>();
for (int i = 0; i < 400; i++)
{
list.Add(i);
}
int [] terms = list.ToArray();
one approach is to fill an array via LINQ
if you want to fill an array with one element
you can simply write
string[] arrayToBeFilled;
arrayToBeFilled= arrayToBeFilled.Append("str").ToArray();
furthermore, If you want to fill an array with multiple elements you can use the
previous code in a loop
//the array you want to fill values in
string[] arrayToBeFilled;
//list of values that you want to fill inside an array
List<string> listToFill = new List<string> { "a1", "a2", "a3" };
//looping through list to start filling the array
foreach (string str in listToFill){
// here are the LINQ extensions
arrayToBeFilled= arrayToBeFilled.Append(str).ToArray();
}
Array Push Example
public void ArrayPush<T>(ref T[] table, object value)
{
Array.Resize(ref table, table.Length + 1); // Resizing the array for the cloned length (+-) (+1)
table.SetValue(value, table.Length - 1); // Setting the value for the new element
}
int[] terms = new int[10]; //create 10 empty index in array terms
//fill value = 400 for every index (run) in the array
//terms.Length is the total length of the array, it is equal to 10 in this case
for (int run = 0; run < terms.Length; run++)
{
terms[run] = 400;
}
//print value from each of the index
for (int run = 0; run < terms.Length; run++)
{
Console.WriteLine("Value in index {0}:\t{1}",run, terms[run]);
}
Console.ReadLine();
/*Output：
Value in index 0: 400
Value in index 1: 400
Value in index 2: 400
Value in index 3: 400
Value in index 4: 400
Value in index 5: 400
Value in index 6: 400
Value in index 7: 400
Value in index 8: 400
Value in index 9: 400
*/
If you don't know the size of the Array or already have an existing array that you are adding to. You can go about this in two ways. The first is using a generic List<T>:
To do this you will want convert the array to a var termsList = terms.ToList(); and use the Add method. Then when done use the var terms = termsList.ToArray(); method to convert back to an array.
var terms = default(int[]);
var termsList = terms == null ? new List<int>() : terms.ToList();
for(var i = 0; i < 400; i++)
termsList.Add(i);
terms = termsList.ToArray();
The second way is resizing the current array:
var terms = default(int[]);
for(var i = 0; i < 400; i++)
{
if(terms == null)
terms = new int[1];
else
Array.Resize<int>(ref terms, terms.Length + 1);
terms[terms.Length - 1] = i;
}
If you are using .NET 3.5 Array.Add(...);
Both of these will allow you to do it dynamically. If you will be adding lots of items then just use a List<T>. If it's just a couple of items then it will have better performance resizing the array. This is because you take more of a hit for creating the List<T> object.
Times in ticks:
3 items
Array Resize Time: 6
List Add Time: 16
400 items
Array Resize Time: 305
List Add Time: 20
I will add this for a another variant. I prefer this type of functional coding lines more.
Enumerable.Range(0, 400).Select(x => x).ToArray();
You can't do this directly. However, you can use Linq to do this:
List<int> termsLst=new List<int>();
for (int runs = 0; runs < 400; runs++)
{
termsLst.Add(runs);
}
int[] terms = termsLst.ToArray();
If the array terms wasn't empty in the beginning, you can convert it to List first then do your stuf. Like:
List<int> termsLst = terms.ToList();
for (int runs = 0; runs < 400; runs++)
{
termsLst.Add(runs);
}
terms = termsLst.ToArray();
Note: don't miss adding 'using System.Linq;' at the begaining of the file.
This seems like a lot less trouble to me:
var usageList = usageArray.ToList();
usageList.Add("newstuff");
usageArray = usageList.ToArray();
Just a different approach:
int runs = 0;
bool batting = true;
string scorecard;
while (batting = runs < 400)
scorecard += "!" + runs++;
return scorecard.Split("!");
int[] terms = new int[400];
for(int runs = 0; runs < 400; runs++)
{
terms[runs] = value;
}
static void Main(string[] args)
{
int[] arrayname = new int[5];/*arrayname is an array of 5 integer [5] mean in array [0],[1],[2],[3],[4],[5] because array starts with zero*/
int i, j;
/*initialize elements of array arrayname*/
for (i = 0; i < 5; i++)
{
arrayname[i] = i + 100;
}
/*output each array element value*/
for (j = 0; j < 5; j++)
{
Console.WriteLine("Element and output value [{0}]={1}",j,arrayname[j]);
}
Console.ReadKey();/*Obtains the next character or function key pressed by the user.
The pressed key is displayed in the console window.*/
}
/*arrayname is an array of 5 integer*/
int[] arrayname = new int[5];
int i, j;
/*initialize elements of array arrayname*/
for (i = 0; i < 5; i++)
{
arrayname[i] = i + 100;
}
To add the list values to string array using C# without using ToArray() method
List<string> list = new List<string>();
list.Add("one");
list.Add("two");
list.Add("three");
list.Add("four");
list.Add("five");
string[] values = new string[list.Count];//assigning the count for array
for(int i=0;i<list.Count;i++)
{
values[i] = list[i].ToString();
}
Output of the value array contains:
one
two
three
four
five
You can do this is with a list. here is how
List<string> info = new List<string>();
info.Add("finally worked");
and if you need to return this array do
return info.ToArray();
Here is one way how to deal with adding new numbers and strings to Array:
int[] ids = new int[10];
ids[0] = 1;
string[] names = new string[10];
do
{
for (int i = 0; i < names.Length; i++)
{
Console.WriteLine("Enter Name");
names[i] = Convert.ToString(Console.ReadLine());
Console.WriteLine($"The Name is: {names[i]}");
Console.WriteLine($"the index of name is: {i}");
Console.WriteLine("Enter ID");
ids[i] = Convert.ToInt32(Console.ReadLine());
Console.WriteLine($"The number is: {ids[i]}");
Console.WriteLine($"the index is: {i}");
}
} while (names.Length <= 10);