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C# simple way to build params list for variable number of params

I have a method that takes this parameter
params string[] additionalParameters
I am building it like this:
qsParams = new string[] {"k=" + k, "l=" + l, "o=" + o, "s=" + s, "t=" + t, "h=" + h, "exp=" + exp };
These are url params. The problem is I only want to add parameters where the variables are not null or empty.
I can do this kind of thing:
if (string.IsNullOrEmpty(k))
{
qsParams = new string[] {"l=" + l, "o=" + o, "s=" + s, "t=" + t, "h=" + h, "exp=" + exp };
}
But that's going to get complicated and ugly trying to handle all the different permutations of empty variables.
Can anyone suggest a simple way to add the params if there are not null? Perhaps a list that I can convert to a params []string?

public static void Main(string[] args)
{
List<string> parameters = new List<string>();
string k = "a";
string l = null;
AddParam("k", k, parameters);
AddParam("l", l, parameters);
string[] result = parameters.ToArray();
}
public static void AddParam(string paramName, string paramValue, List<string> parameters)
{
if (string.IsNullOrEmpty(paramValue))
return;
parameters.Add(paramName + "=" + paramValue);
}
You can try something like this.

You can write a method that returns null if your variable has no value:
private string GetListValue(string prefix, string value) {
if (String.IsNullOrEmpty(value)) {
return null;
}
else {
return prefix + value;
}
}
You can define your raw list with this method (only using 2 values):
string[] rawList = { GetListValue("k=", k), GetListValue("l=", l) };
Then clean the list with LINQ:
string[] cleanValues = rawValues.Where(v => v != null).ToArray();

If your params are always in right order:
List<string> qsParams = new List<string>();
string[] paramNames = new string[] { "k", "l", "o", "s", "t", "h", "exp" };
for (int i = 0; i < additionalParameters.Length; i++)
{
if (!string.IsNullOrEmpty(additionalParameters[i]))
{
qsParams.Add(string.Format("{0}={1}", paramNames[i], additionalParameters[i]));
}
}

Just create a dictionary with the key being the param and the value being well... the value.
Dictionary<string, string> Parameters = new Dictionary<string, string>();
Parameters.Add("k", "myKValue");
Parameters.Add("o", "myOValue");
string paramaterList = string.Join("&", Parameters.Select(x => $"{x.Key}={x.Value}"));
Only add values to the dictionary when they aren't null.

How to merge values of two lists together

For example I have:
public static List<int> actorList = new List<int>();
public static List<string> ipList = new List<string>();
They both have various items in.
So I tried joining the values (string and int) together using a foreach loop:
foreach (string ip in ipList)
{
foreach (int actor in actorList)
{
string temp = ip + " " + actor;
finalList.Add(temp);
}
}
foreach (string final in finalList)
{
Console.WriteLine(finalList);
}
Although looking back at this, this was pretty stupid and obviously will not work, as the first forloop is nested.
My expected values for finalList list:
actorListItem1 ipListItem1
actorListItem2 ipListItem2
actorListItem3 ipListItem3
and so on..
So the values from the two lists are concatenated with each other - corresponding of their position in the lists order.

Use ZIP function of LINQ
List<string> finalList = actorList.Zip(ipList, (x,y) => x + " " + y).ToList();
finalList.ForEach(x=> Console.WriteLine(x)); // For Displaying
OR combine them in one line
actorList.Zip(ipList,(x,y)=>x+" "+y).ToList().ForEach(x=>Console.WriteLine(x));

What about some functional goodness?
listA.Zip(listB, (a, b) => a + " " + b)

Assuming you can use .NET 4, you want to look at the Zip extension method and the provided example:
int[] numbers = { 1, 2, 3, 4 };
string[] words = { "one", "two", "three" };
// The following example concatenates corresponding elements of the
// two input sequences.
var numbersAndWords = numbers.Zip(words, (first, second) => first + " " + second);
foreach (var item in numbersAndWords)
Console.WriteLine(item);
Console.WriteLine();
In this example, because there is no corresponding entry for "4" in words, it is omitted from the output. You would need to do some checking to make sure the collections are the same length before you start.

Loop over the indexes:
for (int i = 0; i < ipList.Count; ++i)
{
string temp = ipList[i] + " " + actorList[i];
finalList.Add(temp);
}
You may also want to add code before this to verify that the lists are the same length:
if (ipList.Count != actorList.Count)
{
// throw some suitable exception
}

for(int i=0; i<actorList.Count; i++)
{
finalList.Add(actorList[i] + " " + ipList[i]);
}

How to check whether a word is composed of other strings in an array

I want to check whether a string is built from another two strings within a given string set.
For example, given the following array:
var arr = new string[] { "b", "at", "bat", "ct", "ll", "ball", "ba"};
I want to return only "bat" and "ball".
That's because they can be composed from two other elements in the array like so:
"bat" = "b" + "at"
"ball" = "ba" + "ll"
I have tried doing it with a foreach loop, but I'm not quite getting it right.
Any help will be much appreciated.
I have done something like
foreach(var x in list)
{
if (dataaccess.IsThreeCharacters(x))
{
for (int i = 0; i < arr.Length; i++)
{
for (int j = i; j < arr.Length; j++)
{
if(x == arr[i] + arr[j])
{
newlist.Add(x);
}
}
}
}
}

This will give you all of the values that can be composed from other values in the sequence:
var values = new HashSet<string>(new[] { "b", "at", "bat", "ct", "ll", "ball", "ba" });
var compositeValues =
from value in values
from otherValue in values
where value != otherValue
let compositeValue = value + otherValue
where values.Contains(compositeValue)
select compositeValue;
Notice the use of HashSet<string>, which gives O(1) lookup performance, as opposed to the O(N) of an array.

This should work although I'm not vouching for efficiency!
static void Main(string[] args)
{
var arr = new string[] { "b", "at", "bat", "ct", "ll", "ball", "ba" };
var composites = from s in arr
from lhs in arr
from rhs in arr
where s == string.Concat(lhs, rhs)
select s;
foreach (var composite in composites)
{
Console.WriteLine(composite);
}
Console.ReadLine();
}

Help with Shannon–Fano coding

Hello I hope some one will help me with this=):
I have a set of some numbers, I need to divide them in two groups with approximately equal sum and assigning the first group with "1", second with "0", then divide each group the same way in to subgroups until subgroups will be one of number from set!
Picture explaining this crazy things):
pict

Here is the basic algorithm, if you know C# it's pretty simple to follow. And the program print the partitions as it explore the tree.
Note that there are some possible bugs and the code is light years away from the quality that a teacher would expect from an homework. (As i guess that it is an homework... if it's for work it's even worse my code would be pretty much Daily-WTF quality)
But it should allow you to understand the basic algorithm structure knowing that :
totalCount does the sum of the Count elements of the collection passed as parameter if you don't know Aggregate.
The other Aggregate usage is there for display, just ignore it.
I commented the sort as multiple elements have the same count and the C# sort function don't preserve order (And i wanted to get the same result as the wikipedia article)
The code:
var symbols = new[] {
new Symbol { Text = "A", Count=15, Probability=double.NaN, Code=""},
new Symbol { Text = "B", Count=7, Probability=double.NaN, Code="" },
new Symbol { Text = "C", Count=6, Probability=double.NaN, Code="" },
new Symbol { Text = "D", Count=6, Probability=double.NaN, Code="" },
new Symbol { Text = "E", Count=5, Probability=double.NaN, Code="" },
}.ToList();
Func<IEnumerable<Symbol>, int> totalCount =
symbols_ => symbols_.Aggregate(0, (a, s) => a + s.Count);
var total = totalCount(symbols);
foreach(var symbol in symbols)
{
symbol.Probability = total / symbol.Count;
}
//symbols.Sort((a, b) => b.Count.CompareTo(a.Count));
// Where is the Y-Combinator when you need it ?
Action<IEnumerable<Symbol>, string, int> recurse = null;
recurse = (symbols_, str, depth) => {
if (symbols_.Count() == 1)
{
symbols_.Single().Code = str;
return;
}
var bestDiff = int.MaxValue;
int i;
for(i = 1; i < symbols_.Count(); i++)
{
var firstPartCount = totalCount(symbols_.Take(i));
var secondPartCount = totalCount(symbols_.Skip(i));
var diff = Math.Abs(firstPartCount - secondPartCount);
if (diff < bestDiff) bestDiff = diff;
else break;
}
i = i - 1;
Console.WriteLine("{0}{1}|{2}", new String('\t', depth),
symbols_.Take(i).Aggregate("", (a, s) => a + s.Text + " "),
symbols_.Skip(i).Aggregate("", (a, s) => a + s.Text + " "));
recurse(symbols_.Take(i), str + "0", depth+1);
recurse(symbols_.Skip(i), str + "1", depth+1);
};
recurse(symbols, "", 0);
Console.WriteLine(new string('-', 78));
foreach (var symbol in symbols)
{
Console.WriteLine("{0}\t{1}\t{2}\t{3}", symbol.Code, symbol.Text,
symbol.Count, symbol.Probability);
}
Console.ReadLine();

C# Permutation of an array of arraylists?

I have an ArrayList[] myList and I am trying to create a list of all the permutations of the values in the arrays.
EXAMPLE: (all values are strings)
myList[0] = { "1", "5", "3", "9" };
myList[1] = { "2", "3" };
myList[2] = { "93" };
The count of myList can be varied so its length is not known beforehand.
I would like to be able to generate a list of all the permutations similar to the following (but with some additional formatting).
1 2 93
1 3 93
5 2 93
5 3 93
3 2 93
3 3 93
9 2 93
9 3 93
Does this make sense of what I am trying to accomplish? I can't seem to come up with a good method for doing this, (if any).
Edit:
I am not sure if recursion would interfere with my desire to format the output in my own manner. Sorry I did not mention before what my formatting was.
I want to end up building a string[] array of all the combinations that follows the format like below:
for the "1 2 93" permutation
I want the output to be "val0=1;val1=2;val2=93;"
I will experiment with recursion for now. Thank you DrJokepu

I'm surprised nobody posted the LINQ solution.
from val0 in new []{ "1", "5", "3", "9" }
from val1 in new []{ "2", "3" }
from val2 in new []{ "93" }
select String.Format("val0={0};val1={1};val2={2}", val0, val1, val2)

Recursive solution
static List<string> foo(int a, List<Array> x)
{
List<string> retval= new List<string>();
if (a == x.Count)
{
retval.Add("");
return retval;
}
foreach (Object y in x[a])
{
foreach (string x2 in foo(a + 1, x))
{
retval.Add(y.ToString() + " " + x2.ToString());
}
}
return retval;
}
static void Main(string[] args)
{
List<Array> myList = new List<Array>();
myList.Add(new string[0]);
myList.Add(new string[0]);
myList.Add(new string[0]);
myList[0] = new string[]{ "1", "5", "3", "9" };
myList[1] = new string[] { "2", "3" };
myList[2] = new string[] { "93" };
foreach (string x in foo(0, myList))
{
Console.WriteLine(x);
}
Console.ReadKey();
}
Note that it would be pretty easy to return a list or array instead of a string by changing the return to be a list of lists of strings and changing the retval.add call to work with a list instead of using concatenation.
How it works:
This is a classic recursive algorithm. The base case is foo(myList.Count, myList), which returns a List containing one element, the empty string. The permutation of a list of n string arrays s1, s2, ..., sN is equal to every member of sA1 prefixed to the permutation of n-1 string arrays, s2, ..., sN. The base case is just there to provide something for each element of sN to be concatenated to.

I recently ran across a similar problem in a project of mine and stumbled on this question. I needed a non-recursive solution that could work with lists of arbitrary objects. Here's what I came up with. Basically I'm forming a list of enumerators for each of the sub-lists and incrementing them iteratively.
public static IEnumerable<IEnumerable<T>> GetPermutations<T>(IEnumerable<IEnumerable<T>> lists)
{
// Check against an empty list.
if (!lists.Any())
{
yield break;
}
// Create a list of iterators into each of the sub-lists.
List<IEnumerator<T>> iterators = new List<IEnumerator<T>>();
foreach (var list in lists)
{
var it = list.GetEnumerator();
// Ensure empty sub-lists are excluded.
if (!it.MoveNext())
{
continue;
}
iterators.Add(it);
}
bool done = false;
while (!done)
{
// Return the current state of all the iterator, this permutation.
yield return from it in iterators select it.Current;
// Move to the next permutation.
bool recurse = false;
var mainIt = iterators.GetEnumerator();
mainIt.MoveNext(); // Move to the first, succeeds; the main list is not empty.
do
{
recurse = false;
var subIt = mainIt.Current;
if (!subIt.MoveNext())
{
subIt.Reset(); // Note the sub-list must be a reset-able IEnumerable!
subIt.MoveNext(); // Move to the first, succeeds; each sub-list is not empty.
if (!mainIt.MoveNext())
{
done = true;
}
else
{
recurse = true;
}
}
}
while (recurse);
}
}

You could use factoradics to generate the enumeration of permutations. Try this article on MSDN for an implementation in C#.

This will work no matter how many arrays you add to your myList:
static void Main(string[] args)
{
string[][] myList = new string[3][];
myList[0] = new string[] { "1", "5", "3", "9" };
myList[1] = new string[] { "2", "3" };
myList[2] = new string[] { "93" };
List<string> permutations = new List<string>(myList[0]);
for (int i = 1; i < myList.Length; ++i)
{
permutations = RecursiveAppend(permutations, myList[i]);
}
//at this point the permutations variable contains all permutations
}
static List<string> RecursiveAppend(List<string> priorPermutations, string[] additions)
{
List<string> newPermutationsResult = new List<string>();
foreach (string priorPermutation in priorPermutations)
{
foreach (string addition in additions)
{
newPermutationsResult.Add(priorPermutation + ":" + addition);
}
}
return newPermutationsResult;
}
Note that it's not really recursive. Probably a misleading function name.
Here is a version that adheres to your new requirements. Note the section where I output to console, this is where you can do your own formatting:
static void Main(string[] args)
{
string[][] myList = new string[3][];
myList[0] = new string[] { "1", "5", "3", "9" };
myList[1] = new string[] { "2", "3" };
myList[2] = new string[] { "93" };
List<List<string>> permutations = new List<List<string>>();
foreach (string init in myList[0])
{
List<string> temp = new List<string>();
temp.Add(init);
permutations.Add(temp);
}
for (int i = 1; i < myList.Length; ++i)
{
permutations = RecursiveAppend(permutations, myList[i]);
}
//at this point the permutations variable contains all permutations
foreach (List<string> list in permutations)
{
foreach (string item in list)
{
Console.Write(item + ":");
}
Console.WriteLine();
}
}
static List<List<string>> RecursiveAppend(List<List<string>> priorPermutations, string[] additions)
{
List<List<string>> newPermutationsResult = new List<List<string>>();
foreach (List<string> priorPermutation in priorPermutations)
{
foreach (string addition in additions)
{
List<string> priorWithAddition = new List<string>(priorPermutation);
priorWithAddition.Add(addition);
newPermutationsResult.Add(priorWithAddition);
}
}
return newPermutationsResult;
}

What you are asking for is called the Cartesian Product. Once you know what its called, there are several similar questions on Stack Overflow. They all seem to end up pointing to an answer which ended up written as a blog post:
http://blogs.msdn.com/b/ericlippert/archive/2010/06/28/computing-a-cartesian-product-with-linq.aspx

Non-recursive solution:
foreach (String s1 in array1) {
foreach (String s2 in array2) {
foreach (String s3 in array3) {
String result = s1 + " " + s2 + " " + s3;
//do something with the result
}
}
}
Recursive solution:
private ArrayList<String> permute(ArrayList<ArrayList<String>> ar, int startIndex) {
if (ar.Count == 1) {
foreach(String s in ar.Value(0)) {
ar.Value(0) = "val" + startIndex + "=" + ar.Value(0);
return ar.Value(0);
}
ArrayList<String> ret = new ArrayList<String>();
ArrayList<String> tmp1 ar.Value(0);
ar.remove(0);
ArrayList<String> tmp2 = permute(ar, startIndex+1);
foreach (String s in tmp1) {
foreach (String s2 in tmp2) {
ret.Add("val" + startIndex + "=" + s + " " + s2);
}
}
return ret;
}

Here is a generic recursive function that I wrote (and an overload that may be convenient to call):
Public Shared Function GetCombinationsFromIEnumerables(ByRef chain() As Object, ByRef IEnumerables As IEnumerable(Of IEnumerable(Of Object))) As List(Of Object())
Dim Combinations As New List(Of Object())
If IEnumerables.Any Then
For Each v In IEnumerables.First
Combinations.AddRange(GetCombinationsFromIEnumerables(chain.Concat(New Object() {v}).ToArray, IEnumerables.Skip(1)).ToArray)
Next
Else
Combinations.Add(chain)
End If
Return Combinations
End Function
Public Shared Function GetCombinationsFromIEnumerables(ByVal ParamArray IEnumerables() As IEnumerable(Of Object)) As List(Of Object())
Return GetCombinationsFromIEnumerables(chain:=New Object() {}, IEnumerables:=IEnumerables.AsEnumerable)
End Function
And the equivalent in C#:
public static List<object[]> GetCombinationsFromIEnumerables(ref object[] chain, ref IEnumerable<IEnumerable<object>> IEnumerables)
{
List<object[]> Combinations = new List<object[]>();
if (IEnumerables.Any) {
foreach ( v in IEnumerables.First) {
Combinations.AddRange(GetCombinationsFromIEnumerables(chain.Concat(new object[] { v }).ToArray, IEnumerables.Skip(1)).ToArray);
}
} else {
Combinations.Add(chain);
}
return Combinations;
}
public static List<object[]> GetCombinationsFromIEnumerables(params IEnumerable<object>[] IEnumerables)
{
return GetCombinationsFromIEnumerables(chain = new object[], IEnumerables = IEnumerables.AsEnumerable);
}
Easy to use:
Dim list1 = New String() {"hello", "bonjour", "hallo", "hola"}
Dim list2 = New String() {"Erwin", "Larry", "Bill"}
Dim list3 = New String() {"!", ".."}
Dim result = MyLib.GetCombinationsFromIEnumerables(list1, list2, list3)
For Each r In result
Debug.Print(String.Join(" "c, r))
Next
or in C#:
object list1 = new string[] {"hello","bonjour","hallo","hola"};
object list2 = new string[] {"Erwin", "Larry", "Bill"};
object list3 = new string[] {"!",".."};
object result = MyLib.GetCombinationsFromIEnumerables(list1, list2, list3);
foreach (r in result) {
Debug.Print(string.Join(' ', r));
}

Here is a version which uses very little code, and is entirely declarative
public static IEnumerable<IEnumerable<T>> GetPermutations<T>(IEnumerable<T> collection) where T : IComparable
{
if (!collection.Any())
{
return new List<IEnumerable<T>>() {Enumerable.Empty<T>() };
}
var sequence = collection.OrderBy(s => s).ToArray();
return sequence.SelectMany(s => GetPermutations(sequence.Where(s2 => !s2.Equals(s))).Select(sq => (new T[] {s}).Concat(sq)));
}

class Program
{
static void Main(string[] args)
{
var listofInts = new List<List<int>>(3);
listofInts.Add(new List<int>{1, 2, 3});
listofInts.Add(new List<int> { 4,5,6 });
listofInts.Add(new List<int> { 7,8,9,10 });
var temp = CrossJoinLists(listofInts);
foreach (var l in temp)
{
foreach (var i in l)
Console.Write(i + ",");
Console.WriteLine();
}
}
private static IEnumerable<List<T>> CrossJoinLists<T>(IEnumerable<List<T>> listofObjects)
{
var result = from obj in listofObjects.First()
select new List<T> {obj};
for (var i = 1; i < listofObjects.Count(); i++)
{
var iLocal = i;
result = from obj in result
from obj2 in listofObjects.ElementAt(iLocal)
select new List<T>(obj){ obj2 };
}
return result;
}
}

Here's a non-recursive, non-Linq solution. I can't help feeling like I could have less looping and calculate the positions with division and modulo, but can't quite wrap my head around that.
static void Main(string[] args)
{
//build test list
List<string[]> myList = new List<string[]>();
myList.Add(new string[0]);
myList.Add(new string[0]);
myList.Add(new string[0]);
myList[0] = new string[] { "1", "2", "3"};
myList[1] = new string[] { "4", "5" };
myList[2] = new string[] { "7", "8", "9" };
object[][] xProds = GetProducts(myList.ToArray());
foreach(object[] os in xProds)
{
foreach(object o in os)
{
Console.Write(o.ToString() + " ");
}
Console.WriteLine();
}
Console.ReadKey();
}
static object[][] GetProducts(object[][] jaggedArray){
int numLists = jaggedArray.Length;
int nProducts = 1;
foreach (object[] oArray in jaggedArray)
{
nProducts *= oArray.Length;
}
object[][] productAry = new object[nProducts][];//holds the results
int[] listIdxArray = new int[numLists];
listIdxArray.Initialize();
int listPtr = 0;//point to current list
for(int rowcounter = 0; rowcounter < nProducts; rowcounter++)
{
//create a result row
object[] prodRow = new object[numLists];
//get values for each column
for(int i=0;i<numLists;i++)
{
prodRow[i] = jaggedArray[i][listIdxArray[i]];
}
productAry[rowcounter] = prodRow;
//move the list pointer
//possible states
// 1) in a list, has room to move down
// 2) at bottom of list, can move to next list
// 3) at bottom of list, no more lists left
//in a list, can move down
if (listIdxArray[listPtr] < (jaggedArray[listPtr].Length - 1))
{
listIdxArray[listPtr]++;
}
else
{
//can move to next column?
//move the pointer over until we find a list, or run out of room
while (listPtr < numLists && listIdxArray[listPtr] >= (jaggedArray[listPtr].Length - 1))
{
listPtr++;
}
if (listPtr < listIdxArray.Length && listIdxArray[listPtr] < (jaggedArray[listPtr].Length - 1))
{
//zero out the previous stuff
for (int k = 0; k < listPtr; k++)
{
listIdxArray[k] = 0;
}
listIdxArray[listPtr]++;
listPtr = 0;
}
}
}
return productAry;
}

One of the problems I encountred when I was doing this for a very large amount of codes was that with the example brian was given I actually run out of memory. To solve this I used following code.
static void foo(string s, List<Array> x, int a)
{
if (a == x.Count)
{
// output here
Console.WriteLine(s);
}
else
{
foreach (object y in x[a])
{
foo(s + y.ToString(), x, a + 1);
}
}
}
static void Main(string[] args)
{
List<Array> a = new List<Array>();
a.Add(new string[0]);
a.Add(new string[0]);
a.Add(new string[0]);
a[0] = new string[] { "T", "Z" };
a[1] = new string[] { "N", "Z" };
a[2] = new string[] { "3", "2", "Z" };
foo("", a, 0);
Console.Read();
}

private static void GetP(List<List<string>> conditions, List<List<string>> combinations, List<string> conditionCombo, List<string> previousT, int selectCnt)
{
for (int i = 0; i < conditions.Count(); i++)
{
List<string> oneField = conditions[i];
for (int k = 0; k < oneField.Count(); k++)
{
List<string> t = new List<string>(conditionCombo);
t.AddRange(previousT);
t.Add(oneField[k]);
if (selectCnt == t.Count )
{
combinations.Add(t);
continue;
}
GetP(conditions.GetRange(i + 1, conditions.Count - 1 - i), combinations, conditionCombo, t, selectCnt);
}
}
}
List<List<string>> a = new List<List<string>>();
a.Add(new List<string> { "1", "5", "3", "9" });
a.Add(new List<string> { "2", "3" });
a.Add(new List<string> { "93" });
List<List<string>> result = new List<List<string>>();
GetP(a, result, new List<string>(), new List<string>(), a.Count);
Another recursive function.