Squaring all elements in a list

Question

I am told to   Write a function  square a   that takes an array  a  of numbers and returns an array containing each of the values of a squared   At first  I had  def square a       for i in a  print i  2   But this does not work since I m printing  and not returning like I was asked  So I tried      def square a           for i in a  return i  2   But this only squares the last number of my array  How can I get it to square the whole list

User · Answer

Use a list comprehension  this is the way to go in pure Python     gt  gt  gt  l    1  2  3  4   gt  gt  gt   i  2 for i in l   1  4  9  16    Or numpy  a well-established module     gt  gt  gt  numpy array  1  2  3  4    2 array   1   4   9  16     In numpy  math operations on arrays are  by default  executed element-wise  That s why you can   2 an entire array there   Other possible solutions would be map-based  but in this case I d really go for the list comprehension  It s Pythonic    and a map-based solution that requires lambdas is slower than LC

User · Answer

You could use a list comprehension   def square list       return  i    2 for i in list    Or you could map it   def square list       return map lambda x  x    2  list    Or you could use a generator  It won t return a list  but you can still iterate through it  and since you don t have to allocate an entire new list  it is possibly more space-efficient than the other options   def square list       for i in list          yield i    2   Or you can do the boring old for-loop  though this is not as idiomatic as some Python programmers would prefer   def square list       ret          for i in list          ret append i    2      return ret

User · Answer

Use numpy   import numpy as np b   list np array a   2

User · Answer

One more map solution   def square a       return map pow  a   2  len a

User · Answer

you can do square list   i  2 for i in start list   which returns  25  9  1  4  16     or  if the list already has values square list extend  i  2 for i in start list      which results in a list that looks like   25  9  1  4  16     Note  you don t want to do square list append  i  2 for i in start list    as it literally adds a list to the original list  such as    original    list    data    25  9  1  4  16

User · Answer

def square a       squares          for i in a          squares append i  2      return squares   so how would i do the square of numbers from 1-20 using the above function

User · Answer

array    1 2 3 4 5  def square array       result   map lambda x  x   x array      return list result  print square array

User · Answer

def square a       squares          for i in a          squares append i  2      return squares

User · Answer

import numpy as np a    2  3  4  np square a

[python] Squaring all elements in a list

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