Writing information from a List of KeyValuePairs into a DataRow

Question

I have the following algorithm which retrieves information in a List of KeyValuePair (prices) and write them in a DataRow. I was wondering if I could achieve the same result without j.

if (prices != null)
{
   for (int i = 8, j=0; j < prices.Count; i+=2, j++) 
   {
      res[i] = prices[j].Value;
      res[i+1] = prices[j].Key;
   }
}

The ouput is a DataRow as follow :

res[8] = prices[0].Value
res[9] = prices[0].Key
res[10] = prices[1].Value
res[11] = prices[1].Key
res[12] = prices[2].Value
res[13] = prices[2].Key

etc.

Answer 1

You can calculate i from j as 2*j + 8 (and 2*j + 9). That would change your code to:

for (int j = 0; j < prices.Count; j++) 
{
   res[2*j + 8] = prices[j].Value;
   res[2*j + 9] = prices[j].Key;
}

Though I'm not sure whether this is actually better code than the original.

Answer 2

I would approach this first by flattening the prices dictionary into a sequence of values eg { Key, Value, Key, Value, Key, Value }.

// This method is returning object for now since I'm not clear what types are in your data row..
IEnumerable<object> Flatten<K, V>(IEnumerable<KeyValuePair<K, V>> pairs)
{
    foreach (var pair in pairs)
    {
        yield return pair.Value;
        yield return pair.Key;
    }
}

Using this I can simply loop over the flattened dictionary and copy the values into the data row:

int offset = 8;
foreach (var x in Flatten(prices))
{
    res[offset++] = x;
}

I suspect there is a far better term than "flatten" for what I'm doing with the dictionary here.