[MAHOUT-1691] iterable of vectors to matrix

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Not A Problem
• Affects Version/s: 0.10.1
• Fix Version/s: 0.11.1
• Component/s: classic
• Labels: math scala
• Assignee: Suneel Marthi
• Reporter: Alexey Grigorev
• Created: 15/Apr/15 16:00
• Updated: 31/Jan/24 22:16
• Resolved: 22/Oct/15 18:07

Description

In Mahout scala bindings, instead of writing

val res = drmX.mapBlock(drmX.ncol) {
  case (keys, block) => {
    val copy = block.like
    copy := block.map(row => (row - mean) / std)
    (keys, copy)
  }
}

I would like to be able to write

val res = drmX.mapBlock(drmX.ncol) {
  case (keys, block) => {
    keys -> block.map(row => (row - mean) / std)
  }
}

Solution: add a method for implicit conversion from iterable to Matrix:

  implicit def iterable2Matrix(that: Iterable[Vector]): Matrix = {
    val first = that.head
    val nrow = that.size
    val ncol = first.size

    val m = if (first.isDense) {
      new DenseMatrix(nrow, ncol)
    } else {
      new SparseRowMatrix(nrow, ncol)
    }

    that.zipWithIndex.foreach { case (row, idx) => 
      m.assignRow(idx.toInt, row)
    }

    m
  }

If it sounds nice, I can send a pull request with this implemented