Menu
While I'm pretty certain that the keys are unordered when returned from linq's ToLookup method, Is the order of values preserved? I can't find any documentation that says one way or the other.
823
The current implementation of ToLookup() does indeed preserve the order of the values (check the implementation of Lookup<TKey,TElement>.
Therefore, by default, PLINQ does not preserve the order of the source sequence. In this regard, PLINQ resembles LINQ to SQL, but is unlike LINQ to Objects, which does preserve ordering.
ToLookup operator in LINQ is an extension method, and it is used to extract a set of key/value pairs from the source. Here, each element in the resultant collection is a generic Lookup object. Lookup object holds the Key and subsequence items that matched with the Key.
Groupby preserves the order of rows within each group. When calling apply, add group keys to index to identify pieces. Reduce the dimensionality of the return type if possible, otherwise return a consistent type.
The current implementation of ToLookup() does indeed preserve the order of the values (check the implementation of Lookup<TKey,TElement>.Grouping<TKey,TElement>.Add()), but I do not believe it is guaranteed to stay that way. To guarantee ordering, your best bet is probably to include the element's original index, perhaps using Select's with-index overload, and then sort again.
85
Yes. According to the documentation:
The values within each group are in the same order as in
source.
35
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
