Python Iterate Dictionary by Index

Question

I want to iterate through a dictionary in python by index number   Example     dict     apple   red   mango   green   orange   orange     I want to iterate through the dictionary from first to last  so that I can access the dictionary items by their indexes  For example  the 1st item will be apple  and the 2nd item will be mango and value will be green   Something like this   for i in range 0 len dict        dict i

User · Accepted Answer

I can t think of any reason why you would want to do that  If you just need to iterate over the dictionary  you can just do   for key  elem in testDict items        print key  elem   OR  for i in testDict       print i  testDict i

User · Answer

Some of the comments are right in saying that these answers do not correspond to the question   One reason one might want to loop through a dictionary using  indexes  is for example to compute a distance matrix for a set of objects in a dictionary  To put it as an example  going a bit to the basics on the bullet below      Assuming one have 1000 objects on a dictionary  the distance square matrix consider all combinations from one object to any other and so it would have dimensions of 1000x1000 elements  But if the distance from object 1 to object 2 is the same as from object 2 to object 1  one need to compute the distance only to less than half of the square matrix  since the diagonal will have distance 0 and the values are mirrored above and below the diagonal    This is why most packages use a condensed distance matrix   How does condensed distance matrix work   pdist     But consider the case one is implementing the computation of a distance matrix  or any kind of permutation of the sort  In such case you need to skip the results from more than half of the cases  This means that a FOR loop that runs through all the dictionary is just hitting an IF and jumping to the next  iteration without performing really any job most of the time  For large datasets this additional  IFs  and loops add up to a relevant amount on the processing time and could be avoided if  at each loop  one starts one  index  further on the dictionary   Going than to the question  my conclusion right now is that the answer is NO  One has no way to directly access the dictionary values by any index except the key or an iterator    I understand that most of the answers up to now applies different approaches to perform this task but really don t allow any index manipulation  that would be useful in a case such as exemplified   The only alternative I see is to use a list or other variable as a sequential index to the dictionary  Here than goes an implementation to exemplify such case      usr bin python3  dishes     spam   4 25   eggs   1 50   sausage   1 75   bacon   2 00  print  Dictionary     n  format dishes    key list   list dishes keys    number of items   len key list   condensed matrix    0  int round   number of items  2 -number of items  2 0   c m index   0  for first index in range 0 number of items       for second index in range first index 1 number of items           condensed matrix c m index    dishes key list first index   - dishes key list second index           print        -         format c m index key list first index  key list second index  condensed matrix c m index            c m index  1   The output is   Dictionary    spam   4 25   eggs   1 5   sausage   1 75   bacon   2 0   0  spam-eggs   2 75 1  spam-sausage   2 5 2  spam-bacon   2 25 3  eggs-sausage   -0 25 4  eggs-bacon   -0 5 5  sausage-bacon   -0 25   Its also worth mentioning that are packages such as intertools that allows one to perform similar tasks in a shorter format

User · Answer

Since you want to iterate in order  you can use sorted   for k  v in sorted dict items         print k v

User · Answer

You can iterate over keys and get values by keys   for key in dict iterkeys        print key  dict key    You can iterate over keys and corresponding values   for key  value in dict iteritems        print key  value   You can use enumerate if you want indexes  remember that dictionaries don t have an order      gt  gt  gt  for index  key in enumerate dict           print index  key      0 orange 1 mango 2 apple  gt  gt  gt

User · Answer

When I need to keep the order  I use a list and a companion dict  color     red   green   orange   fruit     apple  0  mango  1  orange  2  color fruit  apple    for i in range 0 len fruit      or len color      color i   The inconvenience is I don t get easily the fruit from the index  When I need it  I use a tuple  fruitcolor      apple   red     mango   green     orange   orange    index     apple  0  mango  1  orange  2  fruitcolor index  apple    1  for i in range 0 len fruitcolor         fruitcolor i  1  for f  c in fruitcolor      c  Your data structures should be designed to fit your algorithm needs  so that it remains clean  readable and elegant

User · Answer

There are some very good answers here  I d like to add the following here as well   some dict          foo    bar        lorem    ipsum     for index   key  value  in enumerate some dict items         print index  key  value    results in   0 foo bar 1 lorem ipsum   Appears to work with Python 2 7 and 3 5

User · Answer

There are several ways to call the for-loop in python and here what I found so far   A    1 2 3 4  B     col1    1 2 3   col2   4 5 6      Forms of for loop in python    Forms with a list-form  for item in A      print item  print  -----------     for item in B keys        print item  print  -----------     for item in B values        print item  print  -----------     for item in B items        print item      print  The value of keys is    and the value of list of a key is     format item 0  item 1    print  -----------      Results are   1 2 3 4 ----------- col1 col2 -----------  1  2  3   4  5  6  -----------   col1    1  2  3   The value of keys is col1 and the value of list of a key is  1  2  3    col2    4  5  6   The value of keys is col2 and the value of list of a key is  4  5  6  -----------

User · Answer

I wanted to know  idx  key  value  for a python OrderedDict today  mapping of SKUs to quantities in order of the way they should appear on a receipt   The answers here were all bummers    In python 3  at least  this way works and and makes sense   In  1   from collections import OrderedDict         od   OrderedDict           od  a    spam          od  b    ham          od  c    eggs                   for i  k v  in enumerate od items                print   d  s  s   i k v            0 a spam 1 b ham 2 c eggs

User · Answer

Do this   for i in dict keys      dict i

[python] Python Iterate Dictionary by Index

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