code: def __init__(self, block_table, block_expr, source_table, col_key):
      self.col_key = col_key
      first_block = block_expr.take(1)[0]
      self.ncols = first_block.shape[1]
      self.block_table = block_table
      self.block_expr = block_expr
      self.source_table = source_table
  
imports: from typing import List, Tuple
  import hail
  import hail.expr.aggregators
  from hail.expr.expressions import construct_expr
  from hail.expr import expr_float64, expr_call, raise_unless_entry_indexed, matrix_table_source
  from hail import ir
  from hail.table import Table
  from hail.typecheck import typecheck, oneof, nullable
  from hail.utils import FatalError
  from hail.utils.java import Env, info
  from hail.experimental import mt_to_table_of_ndarray
label_desc: Use image node_id 1 to create a new TallSkinnyMatrix object  with example: obj = TallSkinnyMatrix(block_table, block_expr, source_table, col_key)