a!map complex merging

For the updated input map, this change in the Stefan's code should work

a!localVariables(
  local!input:{
    a!map(pagenum: 1,fieldname: "Name", fieldValue:"Appian",docid:1),
    a!map(pagenum: 1,fieldname: "howold", fieldValue:15, docid:1),
    a!map(pagenum: 2,fieldname: "Name", fieldValue:"Java",docid:1),
    a!map(pagenum: 2,fieldname: "howold", fieldValue:25, docid:1),
    a!map(pagenum: 1,fieldname: "Name", fieldValue:"COBOL",docid:2),
    a!map(pagenum: 1,fieldname: "howold", fieldValue:45, docid:2),
    a!map(pagenum: 2,fieldname: "Name", fieldValue:"PL1",docid:2),
    a!map(pagenum: 2,fieldname: "howold", fieldValue:55, docid:2)
  },
  local!uniqueDocRows: a!forEach(
    union(local!input.docid,local!input.docid),
    index(
      local!input,
      where(local!input.docid = fv!item),
      {}
    )
  ),
  a!flatten(a!forEach(
    local!uniqueDocRows,
    a!localVariables(
      local!parentItem: fv!item,
     a!forEach(
    items: union(fv!item.pagenum, fv!item.pagenum),
    expression: a!localVariables(
      local!rows: index(local!parentItem, where(local!parentItem.pagenum = fv!item), {}),
      reduce(
        a!update(_, _, _),
        a!map(pagenum: fv!item),
       merge({local!rows.fieldname,"docid"}, {local!rows.fieldValue, union(local!rows.docid, local!rows.docid)})
     )
  )
)
)
)
)
)

Ps: Wait for Stefan to post the updated solution with better and less complex logic 

Sanchita Gupta Your solution works but it skips first 2 rows , can't see a!map(pagenum: 1 , Name: "Appian", howold: 15, docid:1),in the output

How will it work if you keep on changing inputMap in the question again and again after we post a solution and don't even let us know about that???

For others to know, this was the inputMap updated by you when I answered (for which it works perfectly), before that when Stefan answered it was something else.

From the current map how can you identify that howold:15 is related to Name: "Appian" and not Name: "VB"?

If this list of map is going to remain in the same order i.e., "howold" map will come after every "Name" map, then this code can help.

a!localVariables(
  local!input:{
    a!map(pagenum: 1,fieldname: "Name", fieldValue:"Appian",docid:1),
    a!map(pagenum: 1,fieldname: "howold", fieldValue:15, docid:1),
    a!map(pagenum: 1,fieldname: "Name", fieldValue:"VB",docid:1),
    a!map(pagenum: 1,fieldname: "howold", fieldValue:12, docid:1),
    a!map(pagenum: 2,fieldname: "Name", fieldValue:"Java",docid:1),
    a!map(pagenum: 2,fieldname: "howold", fieldValue:25, docid:1),
    a!map(pagenum: 1,fieldname: "Name", fieldValue:"COBOL",docid:2),
    a!map(pagenum: 1,fieldname: "howold", fieldValue:45, docid:2),
    a!map(pagenum: 2,fieldname: "Name", fieldValue:"PL1",docid:2),
    a!map(pagenum: 2,fieldname: "howold", fieldValue:55, docid:2)
  },
  local!uniqueDocRows: a!forEach(
    union(local!input.docid,local!input.docid),
    index(
      local!input,
      where(local!input.docid = fv!item),
      {}
    )
  ),
  a!flatten(a!forEach(
    local!uniqueDocRows,
    a!localVariables(
      local!parentItem: fv!item,
      a!forEach(
        items: union(fv!item.pagenum, fv!item.pagenum),
        expression: a!localVariables(
          local!Pagenum: fv!item,
          local!rows: index(local!parentItem, where(local!parentItem.pagenum = fv!item), {}),
          local!NameRows: index(local!rows,wherecontains("Name", local!rows.fieldname),null),
          local!howoldRows:  index(local!rows,wherecontains("howold", local!rows.fieldname),null),
          local!finalRows: merge(local!NameRows, local!howoldRows),
          a!forEach(
           local!finalRows,
          reduce(
            a!update(_, _, _),
            a!map(pagenum: local!Pagenum),
            merge({fv!item.fieldname,"docid"}, {fv!item.fieldValue, union(fv!item.docid, fv!item.docid)})
          )
          )
        )
      )
    )
  )
  )
)

It also might help to explain the purpose of this. Then we can develop a more generic algorithm. This feels like you want to translate a list of key-values into a column format.

 Thanks, that fixed it. Sorry the requirements changed and I had to modify inputmap.

@stefan , use case is if u scan a set of documents with multiple pages where u want to extract certain matching key-value pairs ..e.g. document 1 , with 2 pages has multiple matches of certain key/value pairs in terms of fieldName/fieldvalue on page 1 and page 2 .. 

You just sent an email to some Sanchita Gupta twice in a row stating that he/she has been mentioned in this thread which they don't even have any clue about.

Also, it helps if you can mark the answer as verified 

You just sent an email to some Sanchita Gupta twice in a row stating that he/she has been mentioned in this thread which they don't even have any clue about.

Also, it helps if you can mark the answer as verified