book

Lodash Drills

Complete the following Lodash exercises. The goal is to become really good at functional programming paradigm (e.g., _.map, _.filter, _.all, _.any ...etc) and a number of really useful Lodash methods (e.g., _.find, _.pluck ... etc).

  • enter your solution in the solution block
  • utilize lodash functions as much as possible
  • no for/while loop is allowed

Familiarity with programming in this way will not only make you a super productive programmer but also will pave the way for you to learn MapReduce and MongoDB.

Examples

How many people?

Done
Data
[{name: 'John'}, {name: 'Mary'}, {name: 'Joe'}, {name: 'Ben'}]
Expected Output
4
Actual Output
4
Solution
return data.length

What are the names?

Done
Data
[{name: 'John'}, {name: 'Mary'}, {name: 'Joe'}, {name: 'Ben'}]
Expected Output
[
  "John",
  "Mary",
  "Joe",
  "Ben"
]
Actual Output
[
  "John",
  "Mary",
  "Joe",
  "Ben"
]
Solution
return _.map(data, function(d){
    return d.name
})

Exercises

What names begin with the letter J?

Done
Data
[{name: 'John'}, {name: 'Mary'}, {name: 'Joe'}, {name: 'Ben'}]
Expected Output
[
  "John",
  "Joe"
]
Actual Output
[
  "John",
  "Joe"
]
Solution
return _.filter(_.pluck(data, 'name'), function(d){
  return d.match(/J.*/)
})

How many Johns?

Done
Data
[{name: 'John'}, {name: 'John'}, {name: 'John'}, {name: 'Ben'}]
Expected Output
3
Actual Output
3
Solution
return _.size(_.filter(data, function(n){
  return n.name == 'John'
}))

What are all the first names?

Done
Data
[{name: 'John Smith'}, {name: 'Mary Kay'}, {name: 'Peter Pan'}, {name: 'Ben Franklin'}]
Expected Output
[
  "John",
  "Mary",
  "Peter",
  "Ben"
]
Actual Output
[
  "John",
  "Mary",
  "Peter",
  "Ben"
]
Solution
return _.map(data, function(d) {
  return d["name"].split(" ")[0]
})

What are the first names of Smith?

Done
Data
[{name: 'John Smith'}, {name: 'Mary Smith'}, {name: 'Peter Pan'}, {name: 'Ben Smith'}]
Expected Output
[
  "John",
  "Mary",
  "Ben"
]
Actual Output
[
  "John",
  "Mary",
  "Ben"
]
Solution
var smiths = _.filter(data, function(d){
  return d["name"].match(/.*Smith/)
})

return _.map(smiths, function(s){
  return s["name"].split(" ")[0]
})

Change the format to lastname, firstname

Done
Data
[{name: 'John Smith'}, {name: 'Mary Kay'}, {name: 'Peter Pan'}]
Expected Output
[
  {
    "name": "Smith, John"
  },
  {
    "name": "Kay, Mary"
  },
  {
    "name": "Pan, Peter"
  }
]
Actual Output
[
  {
    "name": "Smith, John"
  },
  {
    "name": "Kay, Mary"
  },
  {
    "name": "Pan, Peter"
  }
]
Solution
return _.chain(data)
  .map(function(d) {
    var n = d["name"].split(" ");
      return {"name": n[1] + ', ' + n[0]};
})

How many women?

Done
Data
[{name: 'John Smith', gender: 'm'}, {name: 'Mary Smith', gender: 'f'}, {name: 'Peter Pan', gender: 'm'}, {name: 'Ben Smith', gender: 'm'}]
Expected Output
1
Actual Output
1
Solution
return _.size(_.filter(data, function(d){
  return d.gender == 'f'
}))

How many men whose last name is Smith?

Done
Data
[{name: 'John Smith', gender: 'm'}, {name: 'Mary Smith', gender: 'f'}, {name: 'Peter Pan', gender: 'm'}, {name: 'Ben Smith', gender: 'm'}]
Expected Output
2
Actual Output
2
Solution
var men =  _.filter(data, function(d){
  return d["gender"] == 'm'
})

return _.size(_.filter(men, function(m){
  return m["name"].split(" ")[1] == "Smith"
}))

Done
Data
[{name: 'John Smith', gender: 'm'}, {name: 'Mary Smith', gender: 'f'}, {name: 'Peter Pan', gender: 'm'}, {name: 'Ben Smith', gender: 'm'}]
Expected Output
true
Actual Output
true
Solution
var men =  _.size(_.filter(data, function(d){
  return d.gender == 'm'
}))
var women =  _.size(_.filter(data, function(d){
  return d.gender == 'f'
}))
return (men > women)

What is Peter Pan's gender?

Done
Data
[{name: 'John Smith', gender: 'm'}, {name: 'Mary Smith', gender: 'f'}, {name: 'Peter Pan', gender: 'm'}, {name: 'Ben Smith', gender: 'm'}]
Expected Output
"m"
Actual Output
"m"
Solution
return _.filter(data, function(d){
  return d["name"] == "Peter Pan"
})[0].gender

What is the oldest age?

Done
Data
[{name: 'John Smith', age: 54}, {name: 'Mary Smith', age: 42}, {name: 'Peter Pan', age: 15}, {name: 'Ben Smith', age: 35}]
Expected Output
54
Actual Output
54
Solution
return _.max(_.pluck(data, 'age'))

Is it true everyone is younger than 60?

Done
Data
[{name: 'John Smith', age: 54}, {name: 'Mary Smith', age: 42}, {name: 'Peter Pan', age: 15}, {name: 'Ben Smith', age: 35}]
Expected Output
true
Actual Output
true
Solution
var size = data.length
var l60 = _.size(_.filter(data, function(d){
  return d["age"] < 60
}))

return (size == l60)

Is it true someone is not an adult (younger than 18)?

Done
Data
[{name: 'John Smith', age: 54}, {name: 'Mary Smith', age: 42}, {name: 'Peter Pan', age: 15}, {name: 'Ben Smith', age: 35}]
Expected Output
true
Actual Output
true
Solution
return _.size(_.filter(data, function(d){
  return d["age"] < 18
})) > 0

How many people whose favorites include food?

Done
Data
[{name: 'John Smith', age: 54, favorites: ['food', 'movies']},
 {name: 'Mary Smith', age: 42, favorites: ['food', 'travel']},
 {name: 'Peter Pan', age: 15, favorites: ['minecraft', 'pokemo']},
 {name: 'Ben Smith', age: 35, favorites: ['craft', 'food']}]
Expected Output
3
Actual Output
3
Solution
return _.size(_.filter(_.pluck(data, "favorites"), function(f){
  return f[0] == "food" || f[1] == "food"
}))

Who are over 40 and love travel?

Done
Data
[{name: 'John Smith', age: 54, favorites: ['food', 'movies']},
 {name: 'Mary Smith', age: 42, favorites: ['food', 'travel']},
 {name: 'Peter Pan', age: 15, favorites: ['minecraft', 'pokemo']},
 {name: 'Joe Johnson', age: 46, favorites: ['travel', 'movies']},
 {name: 'Ben Smith', age: 35, favorites: ['craft', 'food']}]
Expected Output
[
  "Mary Smith",
  "Joe Johnson"
]
Actual Output
[
  "Mary Smith",
  "Joe Johnson"
]
Solution
var age = _.filter(data, function(d){
  return d["age"] > 40
})

return _.pluck(_.filter(age, function(a){
  return a["favorites"][0] == 'travel' || a["favorites"][1] == 'travel'
}), "name")

Who is the oldest person loving food?

Done
Data
[{name: 'John Smith', age: 54, favorites: ['food', 'movies']},
 {name: 'Mary Smith', age: 42, favorites: ['food', 'travel']},
 {name: 'Peter Pan', age: 15, favorites: ['minecraft', 'pokemo']},
 {name: 'Joe Johnson', age: 46, favorites: ['travel', 'movies']},
 {name: 'Ben Smith', age: 35, favorites: ['craft', 'food']}]
Expected Output
"John Smith"
Actual Output
"John Smith"
Solution
var food =  _.filter(data, function(d){
    return d["favorites"][0] == "food" || d["favorites"][1] == "food"
  })

return _.last(_.pluck(_.sortBy(food, "age"), "name"))

What are all the unique favorites?

Done
Data
[{name: 'John Smith', age: 54, favorites: ['food', 'movies']},
 {name: 'Mary Smith', age: 42, favorites: ['food', 'travel']},
 {name: 'Peter Pan', age: 15, favorites: ['minecraft', 'pokemo']},
 {name: 'Joe Johnson', age: 46, favorites: ['travel', 'movies']},
 {name: 'Ben Smith', age: 35, favorites: ['craft', 'food']}]
Expected Output
[
  "food",
  "movies",
  "travel",
  "minecraft",
  "pokemo",
  "craft"
]
Actual Output
[
  "food",
  "movies",
  "travel",
  "minecraft",
  "pokemo",
  "craft"
]
Solution
// hint: use _.pluck, _.uniq, _.flatten in some order

return _.uniq(_.flatten(_.pluck(data, 'favorites')))

What are all the unique last names?

Done
Data
[{name: 'John Smith', age: 54, favorites: ['food', 'movies']},
 {name: 'Mary Smith', age: 42, favorites: ['food', 'travel']},
 {name: 'Peter Pan', age: 15, favorites: ['minecraft', 'pokemo']},
 {name: 'Joe Johnson', age: 46, favorites: ['travel', 'movies']},
 {name: 'Ben Smith', age: 35, favorites: ['craft', 'food']}]
Expected Output
[
  "Smith",
  "Pan",
  "Johnson"
]
Actual Output
[
  "Smith",
  "Pan",
  "Johnson"
]
Solution
return _.uniq(_.map(data, function(d) {
  return d["name"].split(" ")[1]
}))