How to resolve the algorithm Hash join step by step in the Nim programming language

Published on 12 May 2024 09:40 PM
#Nim

How to resolve the algorithm Hash join step by step in the Nim programming language

Table of Contents

Problem Statement

An inner join is an operation that combines two data tables into one table, based on matching column values. The simplest way of implementing this operation is the nested loop join algorithm, but a more scalable alternative is the hash join algorithm. Implement the "hash join" algorithm, and demonstrate that it passes the test-case listed below. You should represent the tables as data structures that feel natural in your programming language. The "hash join" algorithm consists of two steps:

In pseudo-code, the algorithm could be expressed as follows: The order of the rows in the output table is not significant. If you're using numerically indexed arrays to represent table rows (rather than referring to columns by name), you could represent the output rows in the form [[27, "Jonah"], ["Jonah", "Whales"]].

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Hash join step by step in the Nim programming language

Source code in the nim programming language

import strformat, tables

type
  Data1 = tuple[value: int; key: string]
  Data2 = tuple[key: string; value: string]

proc `$`(d: Data1 | Data2): string = &"({d[0]}, {d[1]})"

iterator hashJoin(table1: openArray[Data1]; table2: openArray[Data2]): tuple[a: Data1; b: Data2] =
  # Hash phase.
  var h: Table[string, seq[Data1]]
  for s in table1:
    h.mgetOrPut(s.key, @[]).add(s)
  # Join phase.
  for r in table2:
    for s in h[r.key]:
      yield (s, r)


let table1 = [(27, "Jonah"),
              (18, "Alan"),
              (28, "Glory"),
              (18, "Popeye"),
              (28, "Alan")]

let table2 = [("Jonah", "Whales"),
              ("Jonah", "Spiders"),
              ("Alan", "Ghosts"),
              ("Alan", "Zombies"),
              ("Glory", "Buffy")]

for row in hashJoin(table1, table2):
  echo row.a, " ", row.b

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