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How to get arrays intersection include duplicate values at node

array data manupilation data structure lodash node duplicate intersection intersect

Prerequisites

There are two arrays has multiple elements as below.

array1 is

[
  {
    "mail": "shinchi@its-all-writing.com",
    "hobby": "Walking"
  },
  {
    "mail": "shinchi@its-all-writing.com",
    "hobby": "Playing the Bamboo Flute"
  },
  {
    "mail": "kazuyo@its-all-writing.com",
    "hobby": "Reading Books"
  },
  {
    "mail": "foo@its-all-writing.com",
    "hobby": "Driving"
  }
]

array2 is

[
  {
    "mail": "shinchi@its-all-writing.com"
  },
  {
    "mail": "kazuyo@its-all-writing.com"
  },
  {
    "mail": "bar@its-all-writing.com"
  }
]

Then, we want to get this array to be as below.

[
  {
    "mail": "shinchi@its-all-writing.com",
    "hobby": "Walking"
  },
  {
    "mail": "shinchi@its-all-writing.com",
    "hobby": "Playing the Bamboo Flute"
  },
  {
    "mail": "kazuyo@its-all-writing.com",
    "hobby": "Reading Books"
  }
]

lodash provides intersectionBy function. But, if you use it, it returns intersection includes unique values ( is not duplicate ). In this case, intersectionBy returns array to be as below.

const lodash = require('lodash');

let array1 = [
  {
    "mail": "shinchi@its-all-writing.com",
    "hobby": "Walking"
  },
  {
    "mail": "shinchi@its-all-writing.com",
    "hobby": "Playing the Bamboo Flute"
  },
  {
    "mail": "kazuyo@its-all-writing.com",
    "hobby": "Reading Books"
  },
  {
    "mail": "foo@its-all-writing.com",
    "hobby": "Driving"
  }
];

let array2 = [
  {
    "mail": "shinchi@its-all-writing.com"
  },
  {
    "mail": "kazuyo@its-all-writing.com"
  },
  {
    "mail": "bar@its-all-writing.com"
  }
];

let result = lodash.intersectionBy(array1, array2, 'mail');
// =>
// [
//   {
//     "mail": "shinchi@its-all-writing.com",
//     "hobby": "Walking"
//   },
//   {
//     "mail": "kazuyo@its-all-writing.com",
//     "hobby": "Reading Books"
//   }
// ]

Enviroment

  • node

Code

let array1 = [
  {
    "mail": "shinchi@its-all-writing.com",
    "hobby": "Walking"
  },
  {
    "mail": "shinchi@its-all-writing.com",
    "hobby": "Playing the Bamboo Flute"
  },
  {
    "mail": "kazuyo@its-all-writing.com",
    "hobby": "Reading Books"
  },
  {
    "mail": "foo@its-all-writing.com",
    "hobby": "Driving"
  }
];

let array2 = [
  {
    "mail": "shinchi@its-all-writing.com"
  },
  {
    "mail": "kazuyo@its-all-writing.com"
  },
  {
    "mail": "bar@its-all-writing.com"
  }
];

let intersectionWith = function(f, xs, ys) {
  return xs.filter(function(x) {
    return ys.some(function(y) {
      return f(x, y);
    });
  });
};

let equals = function(x,y) {
  return x.mail === y.mail;
};

let result = intersectionWith(equals, array1, array2);
// =>
// [
//   {
//     "mail": "shinchi@its-all-writing.com",
//     "hobby": "Walking"
//   },
//   {
//     "mail": "shinchi@its-all-writing.com",
//     "hobby": "Playing the Bamboo Flute"
//   },
//   {
//     "mail": "kazuyo@its-all-writing.com",
//     "hobby": "Reading Books"
//   }
// ]

Reference