Meta: add new methods

[Athari]

Ideas for new methods to add and example implementations in other libraries.

linq.js

• must: Zip, Concat, Insert, Let, Memoize, MemoizeAll, BufferWithCount, SequenceEqual, Reverse
• high: CascadeBreadthFirst, CascadeDepthFirst, Flatten, Scan, PreScan, Alternate, DefaultIfEmpty, Shuffle
• maybe: Pairwise, PartitionBy, TakeExceptLast, TakeFromLast, Share

Ix

• Defer, Case, DoWhile, If, IsEmpty, (Skip|Take)Last, StartWith, While

MoreLinq

• Batch(Chunk?), Pad, (Skip|Take)Until, (Skip|Take)Every, Zip(Shortest|Longest)

EvenMoreLinq

• Permutations, Subsets, PermutedSubsets, Random, RandomSubset, Slice

LinqLib

• Permutations, Combinations, Statistical

PHP

• Iterators: Recursive*Iterator
• arrays: combine, flip, merge[_recursive], rand, replace[_recursive], walk_recursive, extract

other

• toTable, toCsv, toExcelCsv

P.S. If you need any of these methods or have any other ideas for new features, please let me know. New features aren't high priority until someone actually needs them.

[BLumia]

Would like to leave a +1 for DefaultIfEmpty, which is also in .NET linq API. I think this can be very useful when need to do something like this:

from($ee)->skipWhile($invalidFunc)->average(
    function($p) { return $p['latency']; }
)

Since after skipWhile the data could be empty, calling average() may cause issue, I think DefaultIfEmpty can be useful here.