[jira] [Commented] (MAHOUT-1691) iterable of vectors to matrix

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAHOUT-1691?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14588156#comment-14588156 ] 

ASF GitHub Bot commented on MAHOUT-1691:
----------------------------------------

GitHub user alexeygrigorev opened a pull request:

    https://github.com/apache/mahout/pull/138

    MAHOUT-1691: iterable of vectors to matrix

    Some syntactic sugar for writing 
    
    ```
    val res = drmX.mapBlock(drmX.ncol) {
      case (keys, block) => {
        keys -> block.map(row => (row - mean) / std)
      }
    }
    ```
    
    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)
      }
    }
    ```
    
    When having side effects is not desirable 

You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/alexeygrigorev/mahout it2vec

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/mahout/pull/138.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #138
    
----
commit 1adf6e3e2cdb4ae0dfb25525c61412474bdab8d6
Author: Alexey Grigorev <al...@gmail.com>
Date:   2015-06-16T14:12:50Z

    MAHOUT-1691: iterable of vectors to matrix

----


> iterable of vectors to matrix 
> ------------------------------
>
>                 Key: MAHOUT-1691
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-1691
>             Project: Mahout
>          Issue Type: Improvement
>          Components: Math
>    Affects Versions: 0.10.1
>            Reporter: Alexey Grigorev
>            Priority: Minor
>              Labels: math, scala
>
> In Mahout scala bindings, instead of writing  
> {code}
> val res = drmX.mapBlock(drmX.ncol) {
>   case (keys, block) => {
>     val copy = block.like
>     copy := block.map(row => (row - mean) / std)
>     (keys, copy)
>   }
> }
> {code}
> I would like to be able to write 
> {code}
> val res = drmX.mapBlock(drmX.ncol) {
>   case (keys, block) => {
>     keys -> block.map(row => (row - mean) / std)
>   }
> }
> {code}
> Solution: add a method for implicit conversion from iterable to Matrix:
> {code}
>   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
>   }
> {code}
> If it sounds nice, I can send a pull request with this implemented



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