command_types.txt

- adds columns to each row such that the names and value of the columns are a function of other columns in each row and user input
-- operates: one row at a time
-- input: row, specific column, user input/function
-- output: same row with new column or columns
-- examples:
    ~ addtotals:
        new column name = sum
        new column values = sum other columns
    ~ extract (kv)
        new columns names = keys in other column
        new columns values = values in other columns
    ~ kvform
    ~ outputtext *this is a confusing name since it doesn't do what outputcsv does
    ~ rangemap
    ~ reltime
    ~ rex
    ~ strcat
    ~ tag
    ~ typer
    ~ xmlkv
    ~ xpath
    ~ eval
    ~ spath



TYPES:

commands that operate on one row at a time, adding/transforming columns
- input=in:row
  output=out:row
    ~ addtotals row=true sumfield=f fieldlist=I
        in = (...,(i:numerical)+,...) for i in I
        out = in + (f:numerical=sum_i(i.value))
    ~~ extract (kv)
    ~~ kvform
    ~ outputtext *this is a confusing name since it doesn't do what outputcsv does
    ~ rangemap
    ~ reltime
    ~ rex field=i R
        in = (...,(i:string),...)
        out = in + ((s:string)+) for s in R
    ~ strcat S d
        in = (...,(i:string)+,...) for i in S
        out = in + (d:string=concat_i(i.value)) 
    ~ tag
    ~ typer
    ~ xmlkv
    ~ xpath
    ~ eval d=f:s->t(g1:s,...gk:s)
        in = (...,(g1:s),...,(gk:s),...)
        out = in + (d:t)
    ~ spath
    
commands that operate on a set of rows, adding a row with the same columns as the other rows the end
- input=in:set_of_rows
  output=out:set_of_rows + row
    ~ addcoltotals
    ~ addtotals col=true: 
        in_types: (,...,(numerical,)+...,) fieldlist
        out_types: ()

commands that operate on one row at a time, either returning that row or returning nothing
- input=in:row
  output=out:row|None
    ~ search

commands that operate on all rows, returning fields specified in the command, optionally grouped by field(s)
-