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POTricky LINQ query for text file format transformation
 

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  1. POTricky LINQ query for text file format transformation
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    <p>I have a shopping list in a text file, like this:</p> <pre><code>BuyerId Item; 1; Item1; 1; Item2; 1; ItemN; 2; Item1; 2; ItemN; 3; ItemN; </code></pre> <p>I need to transform this list to a format like this:</p> <pre><code>Item1; Item2; Item3; ...; ItemN &lt;--- For buyer 1 Item1; ...; ItemN &lt;--- For buyer 2 Item1; ...; ItemN &lt;--- For buyer 3 </code></pre> <p>First I parse the CSV file like this:</p> <pre><code>IList&lt;string[]&gt; parsedcsv = (from line in lines.Skip(1) let parsedLine = line.TrimEnd(';').Split(';') select parsedLine).ToList(); </code></pre> <p>Then I group the items with LINQ and aggregate them to the final format:</p> <pre><code>IEnumerable&lt;string&gt; buyers = from entry in parsedcsv group entry by entry[0] into cart select cart.SelectMany(c =&gt; c.Skip(1)) .Aggregate((item1, item2) =&gt; item1 + ";" + item2).Trim(); </code></pre> <p>HOWEVER, as it happens, the BuyerId is not unique, but repeats after a number of times (for example, it can repeat like this: 1,2,3,4,5,1,2,3,4,5,1,2,3 or like this 1,2,3,1,2,3,1,2).</p> <p>No big deal, I could quite easily fix this by grouping the items in a loop that checks that I only deal with one buyer at a time:</p> <pre><code>int lastBatchId = 0; string currentId = parsedcsv[0][0]; for (int i = 0; i &lt; parsedcsv.Count; i++) { bool last = parsedcsv.Count - 1 == i; if (parsedcsv[i][0] != currentId || last) { IEnumerable&lt;string&gt; buyers = from entry in parsedcsv.Skip(lastBatchId) .Take(i - lastBatchId + (last ? 1 : 0)) ... lastBatchId = i; currentId = parsedcsv[i][0]; ... </code></pre> <p>... however, this is not the most elegant solution. I'm almost certain this can be done only with LINQ.</p> <p>Can anyone help me out here please ?</p> <p>Thanks!</p>
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    1. USuser315648
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    1. CO"the buyer with ID = 1 is not the same buyer as the buyer after the buyer with ID = 3." - What is that sentence supposed to mean?
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      1. USDaniel Hilgarth
    2. CO@DanielHilgarth Later on: "HOWEVER, as it happens, the BuyerId is not unique, but repeats after a number of times (for example, it can repeat like this: 1,2,3,4,5,1,2,3,4,5,1,2,3 or like this 1,2,3,1,2,3,1,2)."
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      1. USRawling
    3. COSo, the *value* of the Buyer ID is irrelevant. The only thing that is relevant is the change from one Buyer ID to the next. In that case the loop most certainly is the best way to do this.
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