Search and insert algorithm for this format?

In the end this is what has worked for me, considering the code written above.

public static void busqueda(){ //se llama busqueda pero perfectamente podría llamarse inserción
  String[,] matriz = new Matriz[num1, num2];
  int fila;      

  Boolean marcaEncontrada;
  var marcas = productos.Select(p => p.marca ).Distinct();
 
     for(int lista=0;lista<productos.Count;lista++){
     marcaEncontrada=false;
     for(int i = 0; i<matriz.getLengt(0);i++){ //X
         for(int j = 0; i<getLength(1);j++){   //Y 
              //El IF importante
              if (marcas.Any(m => matriz[i, j].Contains(m)))
              {
                  marcaaEncontrada = compararMarcas(productos[lista].marca, matriz[i, j]);
              }

              if (matriz[i, j].Contains(productos[lista].getProducto() && marcaEncontrada)){
                  fila=i;

              } 
              if(marcaEncontrada && matriz[i,j].Contains(productos.producto)){
              matriz[fila,1] = productos.getStock();
              }
 
          }
      

     }
   }
 }

//Method compareMark

    public static Boolean compararMarca(String marca, String matriz)
    {
        if (!matriz.Contains(marca))
        {
            return false;
        }
        else
        {
            return true;
        }
    }

What "IF IMPORTANTE"it does is compare if the position in the matrix is ​​one of the brands, if it is, it enters the compareBrands method that will return true or false if the brand corresponds to the product whose stock must be entered.

In this way, if in the future it finds a brand that does not correspond to the product to be introduced, it will not be introduced, at the same time that if more products of different brands are added, it will take them into account since we obtain the brand of the product lines before when we give value to marcas.

I leave here the steps that I still hope you understand:

-We put all the products in a list, with attributes where the product, stock and brand attributes are reflected.

-We put all the brands in a list

-As excel can change, we make each cell evaluate if its content is a mark

-If it is, we will enter to check if the brand coincides with that of the product that we are inserting at the moment (which we have previously obtained from our data source)

-If the mark matches we return true, otherwise false.

-With this variable we can make it enter the last conditional, which will enter whenever the band is that of the corresponding brand or not, in case both conditions are met, it will enter the condition and change the value of the cell.

With this I get that:

-If you find a brand other than the one on our list, do not insert where you should not.

-That it correctly finds the row where it should be inserted

-That if more brands are added in the future, the program, without being updated, remains valid.

I would create a dictionary and use it as an index

and it would be the key: brand + product

and in value guard data of the row where it was found: {RowIndex, CellValue}

also adds another benefit, it will be faster

something like that

class RowData
{
  public int RowIndex {get; set;}
  public int CellValue {get; set;}
}

Searching:

crear diccionario ubiacionesxls <string, rowData>
crear lista nuevos : new List<Producto>
//recorrrer filas en excel y cargar items existentes

por cada fila in doc.hoja
  si diccionario no tiene (columna_marca + column_producto)
    agregar ubiacionesxls.add(column_marca + column_producto, new RowData(){ doc.hoja.row, numero_de_celda_valor })
terminar por

//después de cargar el diccionario
//recuperamos lo ultimo en stock
dataReader = repository.GetData(parametros...)

mientras dataReader.read
   var itemkey = datareader.get["column_marca"] + datareader.get["column_pructo"]
   si (ubiacionesxls.containskey(item))
   {
        //actualizamos existentes
        var rowData = ubiacionesxls[item]
        //posicionar en fila celda
        doc.hoja.row = rowData.Row
        doc.hoja.cell = rowData.CellValue
        doc.hoja.SetValue(dataReader.get["column_value"]);
   }
   sino 
   {
       //guardamos el nuevo item para agregar al final del excel
       nuevos.add(new Producto{ Marca = dataReader.get["column_marca"] }, 
       Producto = dataReader.get["column_marca"],
       Stock = dataReader.get["column_value"])
   }
termina mientras

//we load the new ones at the end of the excel sheet

var lastRow = doc.hoja.lastindex;

por cada p in nuevos
{
  doc.hoja.row = lastRow + 1
  doc.hoja.cell = marca_column_index
  doc.hoja.SetValue(dataReader.get["column_marca"]); 

  doc.hoja.cell = marca_column_index
  doc.hoja.SetValue(dataReader.get["column_producto"]);

  doc.hoja.cell = marca_column_index
  doc.hoja.SetValue(dataReader.get["column_stock"]); 
  lastRow++
}