C# LINQ select from list of arrays of strings

Question

I have this data

which is retained in a list of arrays of strings: List<string[]> arrData = new List<string[]>();. The list is filled with the following code:

int columnsCount =4;
int rowsCount = 6;
for (int j = 0; j < columnsCount; j++)
{
    string[] columnData = new string[rowsCount];
    for (int i = 0; i < rowsCount; i++)
        columnData[i] = csv[i][j];
    arrData.Add(columnData);
}

csv[i][j] gives the value for r1c1 etc., so in the end the list has 4 arrays elements, each array having 6 values.

How can I use LINQ to select the yellow rows, meaning that have "a" in the first array, "g" in the second one and "m" in the third?
How can I use LINQ to filter by a list of values in one column (meaning select all rows with "a" or "b" in first column)?

I can alter the code and create a list of lists / dictionaries / whatever is more suitable.

how would you do it without LINQ? Did you even tried anything to achieve this? — MakePeaceGreatAgain
– MakePeaceGreatAgain, Commented Dec 15, 2021 at 16:14
You are making it yourself difficult, because you store the data in columns, instead of rows. Storing it as rows makes it a lot easier. So try to swap the outerloop and innerloop — Jeroen van Langen
– Jeroen van Langen, Commented Dec 15, 2021 at 16:15

Tim Schmelter · Accepted Answer · 2021-12-15 16:22:13Z

1

How can I use LINQ to select the yellow rows, meaning that have "a" in the first array, "g" in the second one and "m" in the third?

IEnumerable<string[]> result = arrData
    .Where(arr => arr?.Length > 2 && arr[0] == "a" && arr[1] == "g" && arr[2] == "m");

How can I use LINQ to filter by a list of values in one column (meaning select all rows with "a" or "b" in first column)?

string[] firstColSearch = { "a", "b" };
IEnumerable<string[]> result = arrData
  .Where(arr => arr?.Length > 0 && firstColSearch.Contains(arr[0]));

edited Dec 15, 2021 at 16:22

answered Dec 15, 2021 at 16:18

Tim Schmelter

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7 Comments

Jeroen van Langen Over a year ago

Did you noticed it is stored as columns? (not rows)

Tim Schmelter Over a year ago

@JeroenvanLangen: I don't think so. I think OP is reading a CSV row by row and value by value and stores them in string-arrays

Jeroen van Langen Over a year ago

It would be easier to store them as rows, so you can select all rows which matches the criteria.

Tim Schmelter Over a year ago

@JeroenvanLangen: But each string[] represents a row and contains all values

adim Over a year ago

Tim Schmelter's solution worked after I switched the list populating code from columns to rows, as Jeroen van Langen proposed.

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