While it may be fine for many cases, If I'm reading the Nectar code correctly, that transpose doesn't guarantee anything about the order of rows within each column. In other words, transposing:
a - b -c d - e - f g - h - i may give you different permutations of "a - d - g" as the first row, depending on shuffle order. You can trivially avoid this with one mapper/reducer, but then you're not exploiting the framework. Note that you can accomplish same with a higher-level language like PIg by using a UDF like LinkedIn's Enumerate [1] to tag each column, and then simply GROUPing BY column number. [1] https://raw.github.com/linkedin/datafu/master/src/java/datafu/pig/bags/Enumerate.java Norbert On Thu, Jun 21, 2012 at 5:00 AM, madhu phatak <phatak....@gmail.com> wrote: > Hi, > Its possible in Map/Reduce. Look into the code here > > https://github.com/zinnia-phatak-dev/Nectar/tree/master/Nectar-regression/src/main/java/com/zinnia/nectar/regression/hadoop/primitive/mapreduce > > > > 2012/6/21 Subir S <subir.sasiku...@gmail.com> > > > Hi, > > > > Is it possible to implement transpose operation of rows into columns and > > vice versa... > > > > > > i.e. > > > > col1 col2 col3 > > col4 col5 col6 > > col7 col8 col9 > > col10 col11 col12 > > > > can this be converted to > > > > col1 col4 col7 col10 > > col2 col5 col8 col11 > > col3 col6 col9 col12 > > > > Is this even possible with map reduce? If yes, which language helps to > > achieve this faster? > > > > Thanks > > > > > > -- > https://github.com/zinnia-phatak-dev/Nectar >
