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(name) {
    if (name[0] == 'J') return true
    else return false
})

How many Johns?

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

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(_.pluck(data, 'name'), function(name) {
    return 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
return _.map(_.filter(_.pluck(data, 'name'), function(name) {
    if (name.split(' ')[1] == 'Smith') return true
    else return false
}), function (name) {
    return 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 _.map(data, function(person) {
    var splitName = person.name.split(' ')
    return {name: splitName[1] + ', ' + splitName[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(_.pluck(data, 'gender'), function(gender) {
    if (gender == 'f') return true
    else return false
}))

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
return _.size(_.filter(data, function(person) {
    if (person.gender == 'm' && person.name.split(' ')[1] == 'Smith') return true
    else return false
}))

Are there more men than 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
true
Actual Output
true
Solution
return _.size(_.filter(_.pluck(data, 'gender'), function(gender) {
    if (gender == 'm') return true
    else return false
})) > _.size(_.filter(_.pluck(data, 'gender'), function(gender) {
    if (gender == 'f') return true
    else return false
}))

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 _.find(data, 'name', 'Peter Pan').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
return _.all(_.pluck(data, 'age'), function(age) {
    if (age < 60) return true
    else return false
})

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 _.some(_.pluck(data, 'age'), function(age) {
    if (age < 18) return true
    else return false
})

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(favorites) {
    return _.includes(favorites, '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
return _.pluck(_.filter(data, function(person) {
    if (person.age > 40 && _.includes(person.favorites, 'travel')) return true
    else return false
}), '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
return _.last(_.sortBy(_.filter(data, function(person) {
    if (_.includes(person.favorites, 'food')) return true
    else return false
}), function(person) {
    return person.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
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(_.flatten(_.map(_.pluck(data, 'name'), function(name) {
    return name.split(' ')[1]
})))