C# compare fields from different lines in csv

Question

I am trying to compare the value in the 0 index of an array on one line and the 0 index on the following line. Imagine a CSV where I have a unique identifier in the first column, a corresponding value in the second column.

USER1, 1P
USER1, 3G
USER2, 1P
USER3, 1V

I would like to check the value of [0] the next line (or previous if that's easier) to compare and if they are the same (as they are in the example) concatenate it to index 1. That is, the data should read as

USER1, 1P, 3G
USER2, 1P
USER3, 1V

before it gets passed onto the next function. So far I have

 private void csvParse(string path)
        {
            using (TextFieldParser parser = new TextFieldParser(path))
                {
                    parser.Delimiters = new string[] { "," };
                    while (!parser.EndOfData)
                    {
                        string[] parts = parser.ReadFields();
                        if (parts == null)
                        {
                            break;
                        }
                        contact.ContactId = parts[0];
                        long nextLine;
                        nextLine = parser.LineNumber+1;
//if line1 parts[0] == line2 parts[0] etc.
                    }
                }
            }

Does anyone have any suggestions? Thank you.

Answer 1

How about saving the array into a variable:

private void csvParse(string path)
        {
            using (TextFieldParser parser = new TextFieldParser(path))
                {
                    parser.Delimiters = new string[] { "," };
                    string[] oldParts = new string[] { string.Empty };
                    while (!parser.EndOfData)
                    {
                        string[] parts = parser.ReadFields();
                        if (parts == null || parts.Length < 1)
                        {
                            break;
                        }

                        if (oldParts[0] == parts[0])
                        {
                             // concat logic goes here
                        }
                        else
                        {
                            contact.ContactId = parts[0];
                        }

                        long nextLine;
                        nextLine = parser.LineNumber+1;
                        oldParts = parts;
//if line1 parts[0] == line2 parts[0] etc.
                    }
                }
            }