What does the map method do in Ruby

Question

I m new to programming  Can someone explain what  map would do in   params    0   param count  map

User · Answer

0  param count means  up to and including param count   0   param count means  up to  but not including param count    Range map does not return an Enumerable  it actually maps it to an array  It s the same as Range to a

User · Answer

Map is a part of the enumerable module  Very similar to  collect  For Example      Class Car      attr accessor  name   model   year      Def initialize  make  model  year         make   model   year   make  model  year     end    end    list        list  lt  lt  Car new  Honda    Accord   2016    list  lt  lt  Car new  Toyota    Camry   2015    list  lt  lt  Car new  Nissan    Altima   2014     p list map   p  p model    Map provides values iterating through an array that are returned by the block parameters

User · Answer

Using ruby 2 4 you can do the same thing using transform values  this feature extracted from rails to ruby   h    a  1  b  2  c  3   h transform values    v  v   10       gt   a  10  b  20  c  30

User · Answer

The map method takes an enumerable object and a block  and runs the block for each element  outputting each returned value from the block  the original object is unchanged unless you use map      1  2  3  map    n  n   n      gt   1  4  9    Array and Range are enumerable types  map with a block returns an Array   map  mutates the original array   Where is this helpful  and what is the difference between map  and each  Here is an example   names     danil    edmund      here we map one array to another  convert each element by some rule names map    name  name capitalize     now names contains   Danil    Edmund    names each    name  puts name     is a programmer      here we just do something with each element   The output   Danil is a programmer Edmund is a programmer

User · Answer

map  along with select and each is one of Ruby s workhorses in my code   It allows you to run an operation on each of your array s objects and return them all in the same place  An example would be to increment an array of numbers by one    1 2 3  map   x  x   1      gt   2 3 4    If you can run a single method on your array s elements you can do it in a shorthand-style like so    To do this with the above example you d have to do something like this  class Numeric   def plusone     self   1   end end  1 2 3  map  amp  plusone     gt   2 3 4   To more simply use the ampersand shortcut technique  let s use a different example     vanessa    david    thomas   map  amp  upcase     gt    VANESSA    DAVID    THOMAS      Transforming data in Ruby often involves a cascade of map operations  Study map  amp  select  they are some of the most useful Ruby methods in the primary library  They re just as important as each    map is also an alias for collect  Use whatever works best for you conceptually    More helpful information   If the Enumerable object you re running each or map on contains a set of Enumerable elements  hashes  arrays   you can declare each of those elements inside your block pipes like so      audi    black   2008     bmw    red   2014   each do  make  color  year    puts  make    make   color    color   year    year   end   Output    make  audi  color  black  year  2008   make  bmw  color  red  year  2014   In the case of a Hash  also an Enumerable object  a Hash is simply an array of tuples with special instructions for the interpreter   The first  pipe parameter  is the key  the second is the value     make   gt   audi    color   gt   black    year   gt  2008  each do  k v      puts    k  is   v   end  make is audi  color is black  year is 2008   To answer the actual question   Assuming that params is a hash  this would be the best way to map through it  Use two block parameters instead of one to capture the key  amp  value pair for each interpreted tuple in the hash   params     one    gt  1   two    gt  2   three    gt  3  params each do  k v    puts    k    v   end   one 1   two 2   three 3

User · Answer

It  maps  a function to each item in an Enumerable - in this case  a range  So it would call the block passed once for every integer from 0 to param count  exclusive - you re right about the dots  and return an array containing each return value   Here s the documentation for Enumerable map  It also has an alias  collect

User · Answer

each   each runs a function for each element in an array  The following two code excerpts are equivalent   x   10   zero    one    two   each  element      x       puts element     x   10 array     zero    one    two    for i in 0  2     x       puts array i  end    map   map applies a function to each element of an array  returning the resulting array  The following are equivalent   array     zero    one    two   newArray   array map  element  element capitalize      array     zero    one    two    newArray      array each  element      newArray  lt  lt  element capitalize        map    map  is like  map  but modifies the array in place  The following are equivalent   array     zero    one    two   array map   element  element capitalize      array     zero    one    two   array   array map  element  element capitalize

[ruby] What does the "map" method do in Ruby?

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