I have to find each subset in a enough big list, 500/1000 items that are positive and negative and are decimal, whiches sum to 0. I'm not an expert so I read many and many articles and solutions, and then I wrote my code. Datas comes from Excel worksheet and I would to mark found sums there.
Code works in this way:
Initally I find all pair that sum to 0
Then I put the remains sums into a list and take the combinations within 20 items, beacause I know the it is not possible bigger combination sum to 0
In these combinations I search if one combinations sums to 0 and save it in result list, else save sum in dictionary as key and then I'll search if dictionary contains next sums (so I check pairs of these subsets)
I keep track of the index so I can reach and modify the cells
To found solutions is enough fast but when I want elaborate the results in Excel become really slow. I don't take care about find all solutions but I want to find as max as possible in a short time.
What do you think about this solution? How can I improve the speed? How can I skip easly the sums that are already taken? And how can mark the cells fastly in my worksheet, beacuse now here is the bottleneck of the program?
I hope it is enough clear :) Thanks to everybody for any help
Here my code of the combination's part:
List<decimal> listDecimal = new List<decimal>();
List<string> listRange = new List<string>();
List<decimal> resDecimal = new List<decimal>();
List<IEnumerable<decimal>> resDecimal2 = new List<IEnumerable<decimal>>();
List<IEnumerable<string>> resIndex = new List<IEnumerable<string>>();
Dictionary<decimal, int> dicSumma = new Dictionary<decimal, int>();
foreach (TarkistaSummat.CellsRemain el in list)
{
decimal sumDec = Convert.ToDecimal(el.Summa.Value);
listDecimal.Add(sumDec);
string row = el.Summa.Cells.Row.ToString();
string col = el.Summa.Cells.Column.ToString();
string range = el.Summa.Cells.Row.ToString() + ":" + el.Summa.Cells.Column.ToString();
listRange.Add(range);
}
var subsets = new List<IEnumerable<decimal>> { new List<decimal>() };
var subsetsIndex = new List<IEnumerable<string>> { new List<string>() };
for (int i = 0; i < list.Count; i++)
{
if (i > 20)
{
List<IEnumerable<decimal>> parSubsets = subsets.GetRange(i, i + 20);
List<IEnumerable<string>> parSubsetsIndex = subsetsIndex.GetRange(i, i + 20);
var Z = parSubsets.Select(x => x.Concat(new[] { listDecimal[i] }));
//var Zfound = Z.Select(x => x).Where(w => w.Sum() ==0);
subsets.AddRange(Z.ToList());
var Zr = parSubsetsIndex.Select(x => x.Concat(new[] { listRange[i] }));
subsetsIndex.AddRange(Zr.ToList());
}
else
{
var T = subsets.Select(y => y.Concat(new[] { listDecimal[i] }));
//var Tfound = T.Select(x => x).Where(w => w.Sum() == 0);
//resDecimal2.AddRange(Tfound);
//var TnotFound = T.Except(Tfound);
subsets.AddRange(T.ToList());
var Tr = subsetsIndex.Select(y => y.Concat(new[] { listRange[i] }));
subsetsIndex.AddRange(Tr.ToList());
}
for (int i = 0; i < subsets.Count; i++)
{
decimal sumDec = subsets[i].Sum();
if (sumDec == 0m)
{
resDecimal2.Add(subsets[i]);
resIndex.Add(subsetsIndex[i]);
continue;
}
else
{
if(dicSumma.ContainsKey(sumDec * -1))
{
dicSumma.TryGetValue(sumDec * -1, out int index);
IEnumerable<decimal> addComb = subsets[i].Union(subsets[index]);
resDecimal2.Add(addComb);
var indexComb = subsetsIndex[i].Union(subsetsIndex[index]);
resIndex.Add(indexComb);
}
else
{
if(!dicSumma.ContainsKey(sumDec))
{
dicSumma.Add(sumDec, i);
}
}
}
}
for (int i = 0; i < resIndex.Count; i++)
{
//List<Range> ranges = new List<Range>();
foreach(string el in resIndex[i])
{
string[] split = el.Split(':');
Range cell = actSheet.Cells[Convert.ToInt32(split[0]), Convert.ToInt32(split[1])];
cell.Interior.ColorIndex = 6;
}
}
}
Related
RowLimit: 4
Example 1:
List with 10 rows
The desired result: 4, 3, 3
Example 2:
List with 9 rows
The desired result: 3, 3, 3
Example 3:
List with 8 rows
The desired result: 4, 4
Example 4:
List with 7 rows
The desired result: 4, 3
At the moment I simply divide the rows according to the rows limit
public List<List<string>> TextWithRowLimit(List<string> TextRows, int RowLimit)
{
List<List<string>> list = new List<List<string>>();
int RowLimitCounter = 1;
List<string> TextRowPackages = new List<string>();
for (int row = 0; row < TextRows.Count; ++row)
{
TextRowPackages.Add($"{TextRows[row]} ");
if (RowLimitCounter == RowLimit)
{
list.Add(TextRowPackages);
RowLimitCounter = 0;
TextRowPackages = new List<string>();
}
RowLimitCounter++;
}
if(TextRowPackages.Count>0)
list.Add(TextRowPackages);
return list;
}
Probably not the prettiest code, but I think this will work for you.
using System.Linq;
using System.Collections.Generic;
public class Program
{
public static void Main()
{
var initialList = Enumerable.Range(1, 10).Select(i => i.ToString()).ToList();
var limit = 4;
var bucketUtility = new BucketUtility();
var list = bucketUtility.TextWithRowLimit(initialList, limit);
}
}
public sealed class BucketUtility
{
public List<List<string>> TextWithRowLimit(List<string> textRows, int rowLimit)
{
var totalRowsCount = textRows.Count;
var remainder = textRows.Count % rowLimit;
var totalBucketsNeeded = remainder == 0 ? totalRowsCount / rowLimit : (totalRowsCount / rowLimit) + 1;
// calculate how many would fill buckets
var initialFillCount = totalBucketsNeeded * rowLimit;
// this can be negative
var remainingToFill = totalRowsCount - initialFillCount;
// size the buckets correctly
var buckets = SizeBuckets(totalBucketsNeeded, rowLimit, remainingToFill);
// assign text values to buckets
int skip = 0;
var result = buckets.Select((bucketSize, i) =>
{
var result = textRows.Select(t => t).Skip(skip).Take(bucketSize).ToList();
skip += bucketSize;
return result;
}).ToList();
return result;
}
private List<int> SizeBuckets(int totalBucketsNeeded, int rowLimit, int remainingToFill)
{
var totalBuckets = Enumerable.Range(0, totalBucketsNeeded).ToList();
var buckets = new List<int>();
for (int i = 0; i < totalBuckets.Count; i++)
{
int bucketSize = rowLimit;
if (remainingToFill > 0)
{
bucketSize++;
remainingToFill--;
}
if (remainingToFill < 0)
{
bucketSize--;
remainingToFill++;
}
buckets.Add(bucketSize);
}
// order them in correct order
return buckets.OrderByDescending(i => i).ToList();
}
}
Can run it here
https://dotnetfiddle.net/CxdHaO
In this code:
for (e = 0; e <= collection.Count - 2; e++)
{
var itm = collection.Read()
var itm_price = itm.Price
var forwards_satisfied_row = collection
.Skip(e + 1)
.SkipWhile(x => x.Price < ex_price)
.FirstOrDefault();
var backwards_satisfied_row = collection
.Reverse()
.Skip(collection.Count - e)
.SkipWhile(x => x.Price < ex_price)
.FirstOrDefault();
}
Suppose the collection contains millions of items and a Reverse() is too expensive, what would be the best way to achieve the same outcome as 'backwards_satisfied_row' ?
Edit:
For each item in the collection, it should find the first preceding item that matches the SkipWhile predicate.
For context I'm finding the distance a price extrema (minima or maxima) is from a horizontal clash with the price. This gives a 'strength' value for each Minima and Maxima, which determines the importance of it, and to help marry it up with extremas of a similar strength.
Edit 2
This chart shows the data in the reproc code below, note the dip in the middle at item #22, this item has a distance of 18.
Bear in mind this operation will be iterated millions of times.
So I'm trying not to read into memory, and to only evaluate the items needed.
When I run this on a large dataset r_ex takes 5 ms per row, whereas l_ex takes up to a second.
It might be tempting to iterate backwards and check that way, but there could be millions of previous records, being read from a binary file.
Many types of searches like Binary search wouldn't be practical here, since the values aren't ordered.
static void Main(string[] args)
{
var dict_dists = new Dictionary<Int32, Int32>();
var dict = new Dictionary<Int32, decimal> {
{1, 410},{2, 474},{3, 431},
{4, 503},{5, 461},{6, 535},
{7, 488},{8, 562},{9, 508},
{10, 582},{11, 522},{12, 593},
{13, 529},{14, 597},{15, 529},
{16, 593},{17, 522},{18, 582},
{19, 510},{20, 565},{21, 492},
{22, 544},{23, 483},{24, 557},
{25, 506},{26, 580},{27, 524},
{28, 598},{29, 537},{30, 609},
{31, 543},{32, 612},{33, 542},
{34, 607},{35, 534},{36, 594},
{37, 518},{38, 572},{39, 496},
{40, 544},{41, 469},{42, 511},
{43, 437},{44, 474},{45, 404},
{46, 462},{47, 427},{48, 485},
{49, 441},{50, 507}};
var i = 0;
for (i = 0; i <= dict.Count - 2; i++)
{
var ele = dict.ElementAt(i);
var current_time = ele.Key;
var current_price = ele.Value;
var is_maxima = current_price > dict.ElementAt(i + 1).Value;
//' If ele.Key = 23 Then here = True
var shortest_dist = Int32.MaxValue;
var l_ex = new KeyValuePair<int, decimal>();
var r_ex = new KeyValuePair<int, decimal>();
if (is_maxima)
{
l_ex = dict.Reverse().Skip(dict.Count - 1 - i + 1).SkipWhile(x => x.Value < current_price).FirstOrDefault();
r_ex = dict.Skip(i + 1).SkipWhile(x => x.Value < current_price).FirstOrDefault();
}
else
{ // 'Is Minima
l_ex = dict.Reverse().Skip(dict.Count - 1 - i + 1).SkipWhile(x => x.Value > current_price).FirstOrDefault();
r_ex = dict.Skip(i + 1).SkipWhile(x => x.Value > current_price).FirstOrDefault();
}
if (l_ex.Key > 0)
{
var l_dist = (current_time - l_ex.Key);
if ( l_dist < shortest_dist ) {
shortest_dist = l_dist;
};
}
if (r_ex.Key > 0)
{
var r_dist = (r_ex.Key - current_time);
if ( r_dist < shortest_dist ) {
shortest_dist = r_dist;
};
}
dict_dists.Add(current_time, shortest_dist);
}
var dist = dict_dists[23];
}
Edit: As a workaround I'm writing a reversed temp file for the left-seekers.
for (i = file.count - 1; i >= 0; i += -1)
{
file.SetPointerToItem(i);
temp_file.Write(file.Read());
}
You could make it more efficient by selecting the precedent of each item in one pass. Lets make an extension method for enumerables that selects a precedent for each element:
public static IEnumerable<T> SelectPrecedent<T>(this IEnumerable<T> source,
Func<T, bool> selector)
{
T selectedPrecedent = default;
foreach (var item in source)
{
if (selector(item)) selectedPrecedent = item;
yield return selectedPrecedent;
}
}
You could then use this method, and select the precedent and the subsequent of each element by doing only two Reverse operations in total:
var precedentArray = collection.SelectPrecedent(x => x.Price < ex_price).ToArray();
var subsequentArray = collection.Reverse()
.SelectPrecedent(x => x.Price < ex_price).Reverse().ToArray();
for (int i = 0; i < collection.Count; i++)
{
var current = collection[i];
var precedent = precedentArray[i];
var subsequent = subsequentArray[i];
// Do something with the current, precedent and subsequent
}
No need to do .Reverse() and then FirstOrDefault(), just use LastOrDefault(). Instead of Skip(collection.Count - e) use .Take(e) elements
var backwards_satisfied_row = collection
.SkipWhile(x => x.Price < ex_price) //Skip till x.Price < ex_price
.Skip(e+1) //Skip first e+1 elements
.LastOrDefault(); //Get Last or default value
You can make your code more efficient by storing collection and then just get FirstOrDefault() and LastOrDefault() for forwards_satisfied_row and backwards_satisfied_row respectively.
like,
for (e = 0; e <= collection.Count - 2; e++)
{
var itm = collection.Read()
var itm_price = itm.Price
var satisfied_rows = collection
.SkipWhile(x => x.Price < ex_price)
.Skip(e + 1)
.ToList();
var forwards_satisfied_row = satisfied_rows.FirstOrDefault();
var backwards_satisfied_row = satisfied_rows.LastOrDefault();
}
I want to be able to fetch .csv files from a folder and plot them up in a chart.
Currently, I'm just saving the files and displaying an individual curve like this:
RunTest function:
public List<Tuple<double,double>> runTest()
{
_dpg = new Root(this, "english", false);
_dpg.Init();
var filename = "Dpg10Export_" + DateTime.Now.ToString("yyyyMMdd_HHmm") + ".csv";
List<Tuple<double, double>> results = new List<Tuple<double, double>>();
var measurement = new Measurement();
var resultCode = RunMeasurement(60, 1000, 2200, ref measurement, null /* TODO: ref ProgressBar? */);
using (var fileStream = new StreamWriter(filename))
{
var count = measurement.I_inc_Values.Count;
for (var i = 0; i < count; i++)
{
var item = measurement.I_inc_Values[i + 1];
var current = (float)Convert.ToDouble(item);
item = measurement.LI_inc_Values[i + 1];
var inductance = (float)Convert.ToDouble(item);
var line = current.ToString() + ";" + inductance.ToString() + ";";
fileStream.WriteLine(line);
currentList.Add(current);
inductanceList.Add(inductance);
results.Add(new Tuple<double, double>(current,inductance));
if (i == 0 || (i + 1) % 32 == 0)
{
Console.WriteLine((i + 1) + ": " + line);
}
}
}
return results;
}
This code produces a csv-file that looks something like this:
0,22 | 0,44
0,32 | 0,54
0,44 | 0,65
And those values produce a curve that looks like this:
When you click on the "get Waveform" button, the curve above is generated. However, I want to display all the curves that has been generated, and a trendline as well. How would I achieve this?
void BindData(List<Tuple<double,double>> results)
{
chart.Series.Clear();
var series1 = new System.Windows.Forms.DataVisualization.Charting.Series
{
Name = "curr/induc",
Color = System.Drawing.Color.Green,
IsVisibleInLegend = true,
IsXValueIndexed = true,
ChartType = SeriesChartType.Line
};
foreach (var i in results)
{
series1.Points.AddXY(i.Item2,i.Item1);
}
chart.Invalidate();
chart.Series.Add(series1);
}
private void getWaveformBtn_Click(object sender, EventArgs e)
{
Dpg10Client.Dpg10Settings settings = new Dpg10Client.Dpg10Settings();
Dpg10Instrument hej = new Dpg10Instrument(settings);
List<Tuple<double,double>> results = hej.runTest();
double current, inductance;
foreach(var i in results)
{
current = i.Item1;
inductance = i.Item2;
textBoxWaveformInput.Text += current.ToString() + inductance.ToString();
}
BindData(results);
}
TL;DR
Parse the information from the CSV files to generate curves, and create a trendline based on those files.
Marked as duplicate: That answer is regarding a straight line, these values can fluctuate in a curve.
There are many ways to solve most of the various problems in your question.
Let me tackle only the one that actually has to do with calculating an average from multiple series, i.e. will not deal with creating a Series with data from a CSV file.
There is a built-in class that can do all sorts of advanced math, both financial and statistical, but I didn't find one that will help in creating an average line/curve over more than one series.
So let's do it ourselves..
The first issue is that to calculate averages we need not just data but the data, that is their x-values, must be grouped into 'bins' from which we want to get the averages.
Unless the data already are grouped like that, e.g. because they have one value per series per day, we need to create such groups.
Let's first collect all the points from all series we want to handle; you may need to adapt the loop to include just your set of series..:
var allPoints = new List <DataPoint>();
for (int s = 0; s < 3; s++) // I know I have created these three series
{
Series ser = chartGraphic.Series["S" + (s+1)];
allPoints.AddRange(ser.Points);
}
Next we need to decide on a bin range/size, that is a value that determines which x-values shall fall into the same bin/group. I chose to have 10 bins.
So we best get the total range of the x-values and divide by the number of bins we want..:
double xmax = allPoints.Max(x => x.XValue);
double xmin = allPoints.Min(x => x.XValue);
int bins = 10;
double groupSize = (xmax - xmin) / (bins - 1);
Next we do the actual math; for this we order our points, group them and select the average for each grouped set..:
var grouped = allPoints
.OrderBy(x => x.XValue)
.GroupBy(x => groupSize * (int)(x.XValue /groupSize ))
.Select(x => new { xval = x.Key, yavg = x.Average(y => y.YValues[0]) })
.ToList();
Now we can add them to a new series to display the averages in the bins:
foreach (var kv in grouped) avgSeries.Points.AddXY(kv.xval + groupSize/2f, kv.yavg);
I center the average point in the bins.
Here is an example:
A few notes on the example:
The average line doesn't show a real 'trend' because my data are pretty much random.
I have added Markers to all series to make the DataPoints stand out from the lines. Here it is how I did it for the averages series:
avgSeries.MarkerStyle = MarkerStyle.Cross;
avgSeries.MarkerSize = 7;
avgSeries.BorderWidth = 2;
I have added a StripLine to show the bins. Here is how:
StripLine sl = new StripLine();
sl.BackColor = Color.FromArgb(44,155,155,222);
sl.StripWidth = groupSize;
sl.Interval = groupSize * 2;
sl.IntervalOffset = chartGraphic.ChartAreas[0].AxisX.IntervalOffset;
chartGraphic.ChartAreas[0].AxisX.StripLines.Add(sl);
I have also set one point to have a really low value of -300 to demonstrate how this will pull down the average in its bin. To keep the chart still nicely centered on the normal range of data I have added a ScaleBreakStyle to the y-axis:
chartGraphic.ChartAreas[0].AxisY.ScaleBreakStyle.BreakLineStyle = BreakLineStyle.Wave;
chartGraphic.ChartAreas[0].AxisY.ScaleBreakStyle.Enabled = true;
I want to take a list of names, add them to an array, then split that array into N groups, then display those arrays in separate textboxes in a Windows form. So far I have this, which takes the list and splits them up, but honestly, I don't think it's doing what I want it to do.
MasterList:
Johnny, Mark, Tom, Carl, Jenny, Susie, Ben, Tim, Angie
Group 1: Johnny, Mark, Angie
Group 2: Tom, Carl
Group 3: Jenny, Susie
Group 4: Ben, Tim
void addnamestoList_Click(object sender, EventArgs e)
{
if (string.IsNullOrWhiteSpace(this.studentnameTboxContent))
{
int num = (int)MessageBox.Show("No content to format.",
"Message",
MessageBoxButtons.OK,
MessageBoxIcon.Exclamation);
}
else
{
transformText();
}
}
public void transformText()
{
string[] masterList = studentnameTboxContent.Split('\n');
var split = from index in Enumerable.Range(0, masterList.Length)
group masterList[index] by index / int.Parse(groupcountTboxContent);
studentNames.Text = "";
foreach (var Array in split)
{
studentNames.AppendText(string.Join(Environment.NewLine, Array.ToArray()));
}
}
Method to randomize list:
private string[] randomizeList(string[] list)
{
Random rnd = new Random();
string[] randomList = list.OrderBy(x => rnd.Next()).ToArray();
return randomList;
}
Here's one way to do it, but it isn't very elegant. Basically calculate the group size based on the group count entered by the user, determine how many items should be in each group, and determine the number of remaining items that need to be added to the first lists (if the group cannot be evenly divided by the count).
Then, in a loop, skip the number of items you've taken so far, then take the group size number of items, and if there are still extra items that need to be added, grab them from the end of the list:
var masterList = new List<string>
{
"Johnny", "Mark", "Tom", "Carl",
"Jenny", "Susie", "Ben", "Tim", "Angie"
};
var groupCount = 4; // Entered by the user
var minGroupSize = masterList.Count / groupCount;
var extraItems = masterList.Count % groupCount;
var groupedNames = new List<List<string>>();
for (int i = 0; i < groupCount; i++)
{
groupedNames.Add(masterList.Skip(i * minGroupSize).Take(minGroupSize).ToList());
if (i < extraItems)
{
groupedNames[i].Add(masterList[masterList.Count - 1 - i]);
}
}
Console.WriteLine("Here are the groups:");
for(int index = 0; index < groupedNames.Count; index++)
{
Console.WriteLine($"#{index + 1}: {string.Join(", ", groupedNames[index])}");
}
Console.Write("\nDone!\nPress any key to exit...");
Console.ReadKey();
Output
This code can easily be extracted into a method so it can be re-used elsewhere:
static List<List<string>> GetGroups(List<string> masterList, int groupCount)
{
var groups = new List<List<string>>();
// Argument validation. All of these conditions should be true.
if (masterList != null && groupCount > 0 && groupCount <= masterList.Count)
{
var minGroupSize = masterList.Count / groupCount;
var extraItems = masterList.Count % groupCount;
for (int i = 0; i < groupCount; i++)
{
groups.Add(masterList.Skip(i * minGroupSize).Take(minGroupSize).ToList());
if (i < extraItems)
{
groups[i].Add(masterList[masterList.Count - 1 - i]);
}
}
}
return groups;
}
Usage
var masterList = new List<string>
{
"Johnny", "Mark", "Tom", "Carl", "Jenny",
"Susie", "Ben", "Tim", "Angie"
};
var groupedNames = GetGroups(masterList, 4);
I'm trying to automate the nested foreach provided that there is a Master List holding List of strings as items for the following scenario.
Here for example I have 5 list of strings held by a master list lstMaster
List<string> lst1 = new List<string> { "1", "2" };
List<string> lst2 = new List<string> { "-" };
List<string> lst3 = new List<string> { "Jan", "Feb" };
List<string> lst4 = new List<string> { "-" };
List<string> lst5 = new List<string> { "2014", "2015" };
List<List<string>> lstMaster = new List<List<string>> { lst1, lst2, lst3, lst4, lst5 };
List<string> lstRes = new List<string>();
foreach (var item1 in lst1)
{
foreach (var item2 in lst2)
{
foreach (var item3 in lst3)
{
foreach (var item4 in lst4)
{
foreach (var item5 in lst5)
{
lstRes.Add(item1 + item2 + item3 + item4 + item5);
}
}
}
}
}
I want to automate the below for loop regardless of the number of list items held by the master list lstMaster
Just do a cross-join with each successive list:
IEnumerable<string> lstRes = new List<string> {null};
foreach(var list in lstMaster)
{
// cross join the current result with each member of the next list
lstRes = lstRes.SelectMany(o => list.Select(s => o + s));
}
results:
List<String> (8 items)
------------------------
1-Jan-2014
1-Jan-2015
1-Feb-2014
1-Feb-2015
2-Jan-2014
2-Jan-2015
2-Feb-2014
2-Feb-2015
Notes:
Declaring lstRes as an IEnumerable<string> prevents the unnecessary creation of additional lists that will be thrown away
with each iteration
The instinctual null is used so that the first cross-join will have something to build on (with strings, null + s = s)
To make this truly dynamic you need two arrays of int loop variables (index and count):
int numLoops = lstMaster.Count;
int[] loopIndex = new int[numLoops];
int[] loopCnt = new int[numLoops];
Then you need the logic to iterate through all these loopIndexes.
Init to start value (optional)
for(int i = 0; i < numLoops; i++) loopIndex[i] = 0;
for(int i = 0; i < numLoops; i++) loopCnt[i] = lstMaster[i].Count;
Finally a big loop that works through all combinations.
bool finished = false;
while(!finished)
{
// access current element
string line = "";
for(int i = 0; i < numLoops; i++)
{
line += lstMaster[i][loopIndex[i]];
}
llstRes.Add(line);
int n = numLoops-1;
for(;;)
{
// increment innermost loop
loopIndex[n]++;
// if at Cnt: reset, increment outer loop
if(loopIndex[n] < loopCnt[n]) break;
loopIndex[n] = 0;
n--;
if(n < 0)
{
finished=true;
break;
}
}
}
public static IEnumerable<IEnumerable<T>> GetPermutations<T>(this IEnumerable<IEnumerable<T>> lists)
{
IEnumerable<IEnumerable<T>> result = new List<IEnumerable<T>> { new List<T>() };
return lists.Aggregate(result, (current, list) => current.SelectMany(o => list.Select(s => o.Union(new[] { s }))));
}
var totalCombinations = 1;
foreach (var l in lstMaster)
{
totalCombinations *= l.Count == 0 ? 1 : l.Count;
}
var res = new string[totalCombinations];
for (int i = 0; i < lstMaster.Count; ++i)
{
var numOfEntries = totalCombinations / lstMaster[i].Count;
for (int j = 0; j < lstMaster[i].Count; ++j)
{
for (int k = numOfEntries * j; k < numOfEntries * (j + 1); ++k)
{
if (res[k] == null)
{
res[k] = lstMaster[i][j];
}
else
{
res[k] += lstMaster[i][j];
}
}
}
}
The algorithm starts from calculating how many combinations we need for all the sub lists.
When we know that we create a result array with exactly this number of entries. Then the algorithm iterates through all the sub lists, extract item from a sub list and calculates how many times the item should occur in the result and adds the item the specified number of times to the results. Moves to next item in the same list and adds to remaining fields (or as many as required if there is more than two items in the list). And it continues through all the sub lists and all the items.
One area though that needs improvement is when the list is empty. There is a risk of DivideByZeroException. I didn't add that. I'd prefer to focus on conveying the idea behind the calculations and didn't want to obfuscate it with additional checks.