How do I convert two lists into a dictionary

Question

Imagine that you have the following list  keys     name    age    food   values     Monty   42   spam    What is the simplest way to produce the following dictionary  a dict     name    Monty    age   42   food    spam

User · Answer

Try this    gt  gt  gt  import itertools  gt  gt  gt  keys     name    age    food    gt  gt  gt  values     Monty   42   spam    gt  gt  gt  adict   dict itertools izip keys values    gt  gt  gt  adict   food    spam    age   42   name    Monty     In Python 2  it s also more economical in memory consumption compared to zip

User · Answer

I had this doubt while I was trying to solve a graph-related problem  The issue I had was I needed to define an empty adjacency list and wanted to initialize all the nodes with an empty list  that s when I thought how about I check if it is fast enough  I mean if it will be worth doing a zip operation rather than simple assignment key-value pair  After all most of the times  the time factor is an important ice breaker  So I performed timeit operation for both approaches   import timeit def dictionary creation n nodes       dummy dict   dict       for node in range n nodes           dummy dict node           return dummy dict   def dictionary creation 1 n nodes       keys   list range n nodes       values       for i in range n nodes       graph   dict zip keys  values       return graph   def wrapper func   args    kwargs       def wrapped            return func  args    kwargs      return wrapped  iteration   wrapper dictionary creation  n nodes  shorthand   wrapper dictionary creation 1  n nodes   for trail in range 1  8       print f Itertion   timeit timeit iteration  number trails   nShorthand   timeit timeit shorthand  number trails       For n nodes   10 000 000 I get   Iteration  2 825081646999024 Shorthand  3 535717916001886  Iteration  5 051560923002398 Shorthand  6 255070794999483  Iteration  6 52859034499852 Shorthand  8 221581164998497  Iteration  8 683652416999394 Shorthand  12 599181543999293  Iteration  11 587241565001023 Shorthand  15 27298851100204  Iteration  14 816342867001367 Shorthand  17 162912737003353  Iteration  16 645022411001264 Shorthand  19 976680120998935  You can clearly see after a certain point  iteration approach at n th step overtakes the time taken by shorthand approach at n-1 th step

User · Answer

Try this    gt  gt  gt  import itertools  gt  gt  gt  keys     name    age    food    gt  gt  gt  values     Monty   42   spam    gt  gt  gt  adict   dict itertools izip keys values    gt  gt  gt  adict   food    spam    age   42   name    Monty     In Python 2  it s also more economical in memory consumption compared to zip

User · Answer

gt  gt  gt  keys     name    age    food    gt  gt  gt  values     Monty   42   spam    gt  gt  gt  dict zip keys  values     food    spam    age   42   name    Monty

User · Answer

If you are working with more than 1 set of values and wish to have a list of dicts you can use this  def as dict list data  list  columns  list       return  dict  zip columns  row    for row in data   Real-life example would be a list of tuples from a db query paired to a tuple of columns from the same query  Other answers only provided for 1 to 1

User · Answer

If you are working with more than 1 set of values and wish to have a list of dicts you can use this  def as dict list data  list  columns  list       return  dict  zip columns  row    for row in data   Real-life example would be a list of tuples from a db query paired to a tuple of columns from the same query  Other answers only provided for 1 to 1

User · Answer

Solution as dictionary comprehension with enumerate   dict    item   values index  for index  item in enumerate keys     Solution as for loop with enumerate   dict      for index  item in enumerate keys       dict item    values index

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with Python 3 x  goes for dict comprehensions  keys     name    age    food   values     Monty   42   spam    dic    k v for k v in zip keys  values    print dic    More on dict comprehensions here  an example is there    gt  gt  gt  print  i   chr 65 i  for i in range 4        0    A   1    B   2    C   3    D

User · Answer

Like this  keys     a    b    c   values    1  2  3  dictionary   dict zip keys  values   print dictionary      a   1   b   2   c   3   Voila  -   The pairwise dict constructor and zip function are awesomely useful

User · Answer

Try this    gt  gt  gt  import itertools  gt  gt  gt  keys     name    age    food    gt  gt  gt  values     Monty   42   spam    gt  gt  gt  adict   dict itertools izip keys values    gt  gt  gt  adict   food    spam    age   42   name    Monty     In Python 2  it s also more economical in memory consumption compared to zip

User · Answer

you can use this below code   dict zip   name    age    food      Monty   42   spam       But make sure that length of the lists will be same if length is not same then zip function turncate the longer one

User · Answer

You may also try with one list which is a combination of two lists     a    1 2 3 4  n    5 6 7 8   x      for i in a n      x append i   print dict zip x 0   x 1

User · Answer

2018-04-18   The best solution is still   In  92   keys     name    age    food        values     Monty   42   spam          In  93   dt   dict zip keys  values   In  94   dt Out 94     age   42   food    spam    name    Monty     Tranpose it       lst      name    Monty      age   42     food    spam        keys  values   zip  lst      In  101   keys     Out 101     name    age    food       In  102   values     Out 102     Monty   42   spam

User · Answer

Here is also an example of adding a list value in you dictionary  list1     Name    Surname    Age   list2      Cyd    JEDD    JESS      DEY    AUDIJE    PONGARON     21  32  47   dic   dict zip list1  list2   print dic    always make sure the your  Key  list1  is always in the first parameter     Name     Cyd    JEDD    JESS     Surname     DEY    AUDIJE    PONGARON     Age    21  32  47

User · Answer

Like this  keys     a    b    c   values    1  2  3  dictionary   dict zip keys  values   print dictionary      a   1   b   2   c   3   Voila  -   The pairwise dict constructor and zip function are awesomely useful

User · Answer

Like this  keys     a    b    c   values    1  2  3  dictionary   dict zip keys  values   print dictionary      a   1   b   2   c   3   Voila  -   The pairwise dict constructor and zip function are awesomely useful

User · Answer

gt  gt  gt  keys     name    age    food    gt  gt  gt  values     Monty   42   spam    gt  gt  gt  dict zip keys  values     food    spam    age   42   name    Monty

User · Answer

You can also use dictionary comprehensions in Python   2 7    gt  gt  gt  keys     name    age    food    gt  gt  gt  values     Monty   42   spam    gt  gt  gt   k  v for k  v in zip keys  values     food    spam    age   42   name    Monty

User · Answer

Solution as dictionary comprehension with enumerate   dict    item   values index  for index  item in enumerate keys     Solution as for loop with enumerate   dict      for index  item in enumerate keys       dict item    values index

User · Answer

If you need to transform keys or values before creating a dictionary then a generator expression could be used  Example    gt  gt  gt  adict   dict  str k   v  for k  v in zip   a   1   b     2   c   3       Take a look Code Like a Pythonista  Idiomatic Python

User · Answer

Although there are multiple ways of doing this but i think most fundamental way of approaching it  creating a loop and dictionary and store values into that dictionary  In the recursive approach the idea is still same it but instead of using a loop  the function called itself until it reaches to the end  Of course there are other approaches like using dict zip key  value   and etc  These aren t the most effective solutions  y    1 2 3 4  x     quot a quot   quot b quot   quot c quot   quot d quot      This below is a brute force method obj      for i in range len y        obj y i     x i  print obj     Recursive approach  obj      def map two lists a b j 0       if j  lt  len a           obj b j     a j          j   1         map two lists a  b  j          return obj          res   map two lists x y  print res    Both the results should print  1   a   2   b   3   c   4   d

User · Answer

You may also try with one list which is a combination of two lists     a    1 2 3 4  n    5 6 7 8   x      for i in a n      x append i   print dict zip x 0   x 1

User · Answer

If you need to transform keys or values before creating a dictionary then a generator expression could be used  Example    gt  gt  gt  adict   dict  str k   v  for k  v in zip   a   1   b     2   c   3       Take a look Code Like a Pythonista  Idiomatic Python

User · Answer

Try this    gt  gt  gt  import itertools  gt  gt  gt  keys     name    age    food    gt  gt  gt  values     Monty   42   spam    gt  gt  gt  adict   dict itertools izip keys values    gt  gt  gt  adict   food    spam    age   42   name    Monty     In Python 2  it s also more economical in memory consumption compared to zip

User · Answer

method without zip function  l1    1 2 3 4 5  l2     a   b   c   d   e   d1      for l1  in l1      for l2  in l2          d1 l1     l2          l2 remove l2           break    print  d1     1   d   2   b   3   e   4   a   5   c

User · Answer

For those who need simple code and aren   t familiar with zip   List1     This    is    a    list   List2     Put    this    into    dictionary     This can be done by one line of code   d    List1 n   List2 n  for n in range len List1

User · Answer

Here is also an example of adding a list value in you dictionary  list1     Name    Surname    Age   list2      Cyd    JEDD    JESS      DEY    AUDIJE    PONGARON     21  32  47   dic   dict zip list1  list2   print dic    always make sure the your  Key  list1  is always in the first parameter     Name     Cyd    JEDD    JESS     Surname     DEY    AUDIJE    PONGARON     Age    21  32  47

User · Answer

gt  gt  gt  keys     name    age    food    gt  gt  gt  values     Monty   42   spam    gt  gt  gt  dict zip keys  values     food    spam    age   42   name    Monty

User · Answer

If you need to transform keys or values before creating a dictionary then a generator expression could be used  Example    gt  gt  gt  adict   dict  str k   v  for k  v in zip   a   1   b     2   c   3       Take a look Code Like a Pythonista  Idiomatic Python

User · Answer

If you need to transform keys or values before creating a dictionary then a generator expression could be used  Example    gt  gt  gt  adict   dict  str k   v  for k  v in zip   a   1   b     2   c   3       Take a look Code Like a Pythonista  Idiomatic Python

User · Answer

Imagine that you have   keys     name    age    food   values     Monty   42   spam         What is the simplest way to produce the following dictionary    dict     name     Monty    age    42   food     spam      Most performant  dict constructor with zip  new dict   dict zip keys  values     In Python 3  zip now returns a lazy iterator  and this is now the most performant approach   dict zip keys  values   does require the one-time global lookup each for dict and zip  but it doesn t form any unnecessary intermediate data-structures or have to deal with local lookups in function application   Runner-up  dict comprehension   A close runner-up to using the dict constructor is to use the native syntax of a dict comprehension  not a list comprehension  as others have mistakenly put it    new dict    k  v for k  v in zip keys  values     Choose this when you need to map or filter based on the keys or value   In Python 2  zip returns a list  to avoid creating an unnecessary list  use izip instead  aliased to zip can reduce code changes when you move to Python 3    from itertools import izip as zip   So that is still  2 7    new dict    k  v for k  v in zip keys  values     Python 2  ideal for  lt   2 6  izip from itertools becomes zip in Python 3  izip is better than zip for Python 2  because it avoids the unnecessary list creation   and ideal for 2 6 or below   from itertools import izip new dict   dict izip keys  values     Result for all cases   In all cases    gt  gt  gt  new dict   age   42   name    Monty    food    spam     Explanation   If we look at the help on dict we see that it takes a variety of forms of arguments     gt  gt  gt  help dict   class dict object      dict   - gt  new empty dictionary     dict mapping  - gt  new dictionary initialized from a mapping object s          key  value  pairs     dict iterable  - gt  new dictionary initialized as if via          d              for k  v in iterable              d k    v     dict   kwargs  - gt  new dictionary initialized with the name value pairs         in the keyword argument list   For example   dict one 1  two 2     The optimal approach is to use an iterable while avoiding creating unnecessary data structures  In Python 2  zip creates an unnecessary list    gt  gt  gt  zip keys  values     name    Monty      age   42     food    spam      In Python 3  the equivalent would be    gt  gt  gt  list zip keys  values      name    Monty      age   42     food    spam      and Python 3 s zip merely creates an iterable object    gt  gt  gt  zip keys  values   lt zip object at 0x7f0e2ad029c8 gt    Since we want to avoid creating unnecessary data structures  we usually want to avoid Python 2 s zip  since it creates an unnecessary list    Less performant alternatives   This is a generator expression being passed to the dict constructor   generator expression     k  v  for k  v in zip keys  values   dict generator expression    or equivalently   dict  k  v  for k  v in zip keys  values     And this is a list comprehension being passed to the dict constructor   dict   k  v  for k  v in zip keys  values      In the first two cases  an extra layer of non-operative  thus unnecessary  computation is placed over the zip iterable  and in the case of the list comprehension  an extra list is unnecessarily created  I would expect all of them to be less performant  and certainly not more-so   Performance review   In 64 bit Python 3 8 2 provided by Nix  on Ubuntu 16 04  ordered from fastest to slowest    gt  gt  gt  min timeit repeat lambda  dict zip keys  values     0 6695233230129816  gt  gt  gt  min timeit repeat lambda   k  v for k  v in zip keys  values     0 6941362579818815  gt  gt  gt  min timeit repeat lambda   keys i   values i  for i in range len keys      0 8782548159942962  gt  gt  gt    gt  gt  gt  min timeit repeat lambda  dict   k  v  for k  v in zip keys  values      1 077607496001292  gt  gt  gt  min timeit repeat lambda  dict  k  v  for k  v in zip keys  values     1 1840861019445583   dict zip keys  values   wins even with small sets of keys and values  but for larger sets  the differences in performance will become greater   A commenter said      min seems like a bad way to compare performance  Surely mean and or max would be much more useful indicators for real usage    We use min because these algorithms are deterministic  We want to know the performance of the algorithms under the best conditions possible    If the operating system hangs for any reason  it has nothing to do with what we re trying to compare  so we need to exclude those kinds of results from our analysis   If we used mean  those kinds of events would skew our results greatly  and if we used max we will only get the most extreme result - the one most likely affected by such an event   A commenter also says      In python 3 6 8  using mean values  the dict comprehension is indeed still faster  by about 30  for these small lists  For larger lists  10k random numbers   the dict call is about 10  faster     I presume we mean dict zip     with 10k random numbers  That does sound like a fairly unusual use case  It does makes sense that the most direct calls would dominate in large datasets  and I wouldn t be surprised if OS hangs are dominating given how long it would take to run that test  further skewing your numbers  And if you use mean or max I would consider your results meaningless   Let s use a more realistic size on our top examples   import numpy import timeit l1   list numpy random random 100   l2   list numpy random random 100     And we see here that dict zip     does indeed run faster for larger datasets by about 20     gt  gt  gt  min timeit repeat lambda   k  v for k  v in zip l1  l2     9 698965263989521  gt  gt  gt  min timeit repeat lambda  dict zip l1  l2     7 9965161079890095

User · Answer

Imagine that you have   keys     name    age    food   values     Monty   42   spam         What is the simplest way to produce the following dictionary    dict     name     Monty    age    42   food     spam      Most performant  dict constructor with zip  new dict   dict zip keys  values     In Python 3  zip now returns a lazy iterator  and this is now the most performant approach   dict zip keys  values   does require the one-time global lookup each for dict and zip  but it doesn t form any unnecessary intermediate data-structures or have to deal with local lookups in function application   Runner-up  dict comprehension   A close runner-up to using the dict constructor is to use the native syntax of a dict comprehension  not a list comprehension  as others have mistakenly put it    new dict    k  v for k  v in zip keys  values     Choose this when you need to map or filter based on the keys or value   In Python 2  zip returns a list  to avoid creating an unnecessary list  use izip instead  aliased to zip can reduce code changes when you move to Python 3    from itertools import izip as zip   So that is still  2 7    new dict    k  v for k  v in zip keys  values     Python 2  ideal for  lt   2 6  izip from itertools becomes zip in Python 3  izip is better than zip for Python 2  because it avoids the unnecessary list creation   and ideal for 2 6 or below   from itertools import izip new dict   dict izip keys  values     Result for all cases   In all cases    gt  gt  gt  new dict   age   42   name    Monty    food    spam     Explanation   If we look at the help on dict we see that it takes a variety of forms of arguments     gt  gt  gt  help dict   class dict object      dict   - gt  new empty dictionary     dict mapping  - gt  new dictionary initialized from a mapping object s          key  value  pairs     dict iterable  - gt  new dictionary initialized as if via          d              for k  v in iterable              d k    v     dict   kwargs  - gt  new dictionary initialized with the name value pairs         in the keyword argument list   For example   dict one 1  two 2     The optimal approach is to use an iterable while avoiding creating unnecessary data structures  In Python 2  zip creates an unnecessary list    gt  gt  gt  zip keys  values     name    Monty      age   42     food    spam      In Python 3  the equivalent would be    gt  gt  gt  list zip keys  values      name    Monty      age   42     food    spam      and Python 3 s zip merely creates an iterable object    gt  gt  gt  zip keys  values   lt zip object at 0x7f0e2ad029c8 gt    Since we want to avoid creating unnecessary data structures  we usually want to avoid Python 2 s zip  since it creates an unnecessary list    Less performant alternatives   This is a generator expression being passed to the dict constructor   generator expression     k  v  for k  v in zip keys  values   dict generator expression    or equivalently   dict  k  v  for k  v in zip keys  values     And this is a list comprehension being passed to the dict constructor   dict   k  v  for k  v in zip keys  values      In the first two cases  an extra layer of non-operative  thus unnecessary  computation is placed over the zip iterable  and in the case of the list comprehension  an extra list is unnecessarily created  I would expect all of them to be less performant  and certainly not more-so   Performance review   In 64 bit Python 3 8 2 provided by Nix  on Ubuntu 16 04  ordered from fastest to slowest    gt  gt  gt  min timeit repeat lambda  dict zip keys  values     0 6695233230129816  gt  gt  gt  min timeit repeat lambda   k  v for k  v in zip keys  values     0 6941362579818815  gt  gt  gt  min timeit repeat lambda   keys i   values i  for i in range len keys      0 8782548159942962  gt  gt  gt    gt  gt  gt  min timeit repeat lambda  dict   k  v  for k  v in zip keys  values      1 077607496001292  gt  gt  gt  min timeit repeat lambda  dict  k  v  for k  v in zip keys  values     1 1840861019445583   dict zip keys  values   wins even with small sets of keys and values  but for larger sets  the differences in performance will become greater   A commenter said      min seems like a bad way to compare performance  Surely mean and or max would be much more useful indicators for real usage    We use min because these algorithms are deterministic  We want to know the performance of the algorithms under the best conditions possible    If the operating system hangs for any reason  it has nothing to do with what we re trying to compare  so we need to exclude those kinds of results from our analysis   If we used mean  those kinds of events would skew our results greatly  and if we used max we will only get the most extreme result - the one most likely affected by such an event   A commenter also says      In python 3 6 8  using mean values  the dict comprehension is indeed still faster  by about 30  for these small lists  For larger lists  10k random numbers   the dict call is about 10  faster     I presume we mean dict zip     with 10k random numbers  That does sound like a fairly unusual use case  It does makes sense that the most direct calls would dominate in large datasets  and I wouldn t be surprised if OS hangs are dominating given how long it would take to run that test  further skewing your numbers  And if you use mean or max I would consider your results meaningless   Let s use a more realistic size on our top examples   import numpy import timeit l1   list numpy random random 100   l2   list numpy random random 100     And we see here that dict zip     does indeed run faster for larger datasets by about 20     gt  gt  gt  min timeit repeat lambda   k  v for k  v in zip l1  l2     9 698965263989521  gt  gt  gt  min timeit repeat lambda  dict zip l1  l2     7 9965161079890095

User · Answer

method without zip function  l1    1 2 3 4 5  l2     a   b   c   d   e   d1      for l1  in l1      for l2  in l2          d1 l1     l2          l2 remove l2           break    print  d1     1   d   2   b   3   e   4   a   5   c

User · Answer

gt  gt  gt  keys     name    age    food    gt  gt  gt  values     Monty   42   spam    gt  gt  gt  dict zip keys  values     food    spam    age   42   name    Monty

User · Answer

Like this  keys     a    b    c   values    1  2  3  dictionary   dict zip keys  values   print dictionary      a   1   b   2   c   3   Voila  -   The pairwise dict constructor and zip function are awesomely useful

User · Answer

You can also use dictionary comprehensions in Python   2 7    gt  gt  gt  keys     name    age    food    gt  gt  gt  values     Monty   42   spam    gt  gt  gt   k  v for k  v in zip keys  values     food    spam    age   42   name    Monty

User · Answer

Although there are multiple ways of doing this but i think most fundamental way of approaching it  creating a loop and dictionary and store values into that dictionary  In the recursive approach the idea is still same it but instead of using a loop  the function called itself until it reaches to the end  Of course there are other approaches like using dict zip key  value   and etc  These aren t the most effective solutions  y    1 2 3 4  x     quot a quot   quot b quot   quot c quot   quot d quot      This below is a brute force method obj      for i in range len y        obj y i     x i  print obj     Recursive approach  obj      def map two lists a b j 0       if j  lt  len a           obj b j     a j          j   1         map two lists a  b  j          return obj          res   map two lists x y  print res    Both the results should print  1   a   2   b   3   c   4   d

User · Answer

A more natural way is to use dictionary comprehension   keys     name    age    food   values     Monty   42   spam       dict    keys i   values i  for i in range len keys

User · Answer

you can use this below code   dict zip   name    age    food      Monty   42   spam       But make sure that length of the lists will be same if length is not same then zip function turncate the longer one

User · Answer

A more natural way is to use dictionary comprehension   keys     name    age    food   values     Monty   42   spam       dict    keys i   values i  for i in range len keys

User · Answer

2018-04-18   The best solution is still   In  92   keys     name    age    food        values     Monty   42   spam          In  93   dt   dict zip keys  values   In  94   dt Out 94     age   42   food    spam    name    Monty     Tranpose it       lst      name    Monty      age   42     food    spam        keys  values   zip  lst      In  101   keys     Out 101     name    age    food       In  102   values     Out 102     Monty   42   spam

User · Answer

I had this doubt while I was trying to solve a graph-related problem  The issue I had was I needed to define an empty adjacency list and wanted to initialize all the nodes with an empty list  that s when I thought how about I check if it is fast enough  I mean if it will be worth doing a zip operation rather than simple assignment key-value pair  After all most of the times  the time factor is an important ice breaker  So I performed timeit operation for both approaches   import timeit def dictionary creation n nodes       dummy dict   dict       for node in range n nodes           dummy dict node           return dummy dict   def dictionary creation 1 n nodes       keys   list range n nodes       values       for i in range n nodes       graph   dict zip keys  values       return graph   def wrapper func   args    kwargs       def wrapped            return func  args    kwargs      return wrapped  iteration   wrapper dictionary creation  n nodes  shorthand   wrapper dictionary creation 1  n nodes   for trail in range 1  8       print f Itertion   timeit timeit iteration  number trails   nShorthand   timeit timeit shorthand  number trails       For n nodes   10 000 000 I get   Iteration  2 825081646999024 Shorthand  3 535717916001886  Iteration  5 051560923002398 Shorthand  6 255070794999483  Iteration  6 52859034499852 Shorthand  8 221581164998497  Iteration  8 683652416999394 Shorthand  12 599181543999293  Iteration  11 587241565001023 Shorthand  15 27298851100204  Iteration  14 816342867001367 Shorthand  17 162912737003353  Iteration  16 645022411001264 Shorthand  19 976680120998935  You can clearly see after a certain point  iteration approach at n th step overtakes the time taken by shorthand approach at n-1 th step

User · Answer

with Python 3 x  goes for dict comprehensions  keys     name    age    food   values     Monty   42   spam    dic    k v for k v in zip keys  values    print dic    More on dict comprehensions here  an example is there    gt  gt  gt  print  i   chr 65 i  for i in range 4        0    A   1    B   2    C   3    D

User · Answer

For those who need simple code and aren   t familiar with zip   List1     This    is    a    list   List2     Put    this    into    dictionary     This can be done by one line of code   d    List1 n   List2 n  for n in range len List1

[python] How do I convert two lists into a dictionary?

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