Getting a list of values from a list of dicts

Question

I have a list of dicts like this      value    apple    blah   2       value    banana    blah   3        value    cars    blah   4     I want   apple    banana    cars    Whats the best way to do this

User · Answer

A very simple way to do it is   list1      j 0 for i in com list      if j  0          list1 0   i  value        else          list1 append i  value        j  1   Output        apple    banana    cars

User · Answer

Follow the example --  songs       title    happy birthday    playcount   4     title    AC DC    playcount   2     title    Billie Jean    playcount   6     title    Human Touch    playcount   3     print                                print f Songs -- gt   songs   n   title   list map lambda x   x  title    songs   print f Print Title -- gt   title     playcount   list map lambda x   x  playcount    songs   print f Print Playcount -- gt   playcount    print  f Print Sorted playcount -- gt   sorted playcount        Aliter - print sorted list map lambda x  x  playcount   songs

User · Answer

For a very simple case like this  a comprehension  as in Ismail Badawi s answer is definitely the way to go   But when things get more complicated  and you need to start writing multi-clause or nested comprehensions with complex expressions in them  it s worth looking into other alternatives  There are a few different  quasi- standard ways to specify XPath-style searches on nested dict-and-list structures  such as JSONPath  DPath  and KVC  And there are nice libraries on PyPI for them   Here s an example with the library named dpath  showing how it can simplify something just a bit more complicated    gt  gt  gt  dd              fruits      value    apple    blah   2     value    banana    blah   3             vehicles      value    cars    blah  4      gt  gt  gt   key     value   d  value    for d in value  for key  value in dd items      fruits      value    apple      value    banana       vehicles      value    cars       gt  gt  gt  dpath util search dd       value     fruits      value    apple      value    banana       vehicles      value    cars       Or  using jsonpath-ng    gt  gt  gt   d  value   for key  value in dd items   for d in value    apple    banana    cars    gt  gt  gt   m value for m in jsonpath ng parse        value   find dd     apple    banana    cars     This one may not look quite as simple at first glance  because find returns match objects  which include all kinds of things besides just the matched value  such as a path directly to each item  But for more complex expressions  being able to specify a path like        value  instead of a comprehension clause for each   can make a big difference  Plus  JSONPath is a language-agnostic specification  and there are even online testers that can be very handy for debugging

User · Answer

Please try out this one  d     value    apple    blah   2      value    banana    blah   3      value     cars    blah   4    b d 0   value   c d 1   value   d d 2   value   new list  b c d  print new list   Output    apple    banana    cars

User · Answer

Assuming every dict has a value key  you can write  assuming your list is named l    d  value   for d in l    If value might be missing  you can use   d  value   for d in l if  value  in d

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x  value   for x in list of dicts

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Here s another way to do it using map   and lambda functions   gt  gt  gt  map lambda d  d  value    l   where l is the list  I see this way  quot sexiest quot   but I would do it using the list comprehension  Update  In case that  value  might be missing as a key use   gt  gt  gt  map lambda d  d get  value    default value    l   Update  I m also not a big fan of lambdas  I prefer to name things    this is how I would do it with that in mind   gt  gt  gt  import operator  gt  gt  gt  get value   operator itemgetter  value    gt  gt  gt  map get value  l   I would even go further and create a sole function that explicitly says what I want to achieve   gt  gt  gt  import operator  functools  gt  gt  gt  get value   operator itemgetter  value    gt  gt  gt  get values   functools partial map  get value   gt  gt  gt  get values l        lt list of values gt    With Python 3  since map returns an iterator  use list to return a list  e g  list map operator itemgetter  value    l

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Get key values from list of dictionaries in python    Get key values from list of dictionaries in python    Ex   data       obj1     cpu percentage   15    ram  3  memory percentage   66         obj2      cpu percentage   0   ram  4  memory percentage   35         for d in data      for key value in d items            z   key    cpu percentage   d  cpu percentage    memory percentage   d  memory percentage    for d in value         print z    Output     obj1     cpu percentage    15     memory percentage    66       obj2     cpu percentage    0    memory percentage    35

User · Answer

I think as simple as below would give you what you are looking for   In 5   ll      value    apple    blah   2     value    banana    blah   3      value    cars    blah  4   In 6   ld    d get  value   None  for d in ll  In 7   ld Out 7     apple    banana    cars     You can do this with a combination of map and lambda as well but list comprehension looks more elegant and pythonic   For a smaller input list comprehension is way to go but if the input is really big then i guess generators are the ideal way   In 11   gd    d get  value   None  for d in ll  In 12   gd Out 12    lt generator object  lt genexpr gt  at 0x7f5774568b10 gt  In 13    -  join gd  Out 13    apple-banana-cars    Here is a comparison of all possible solutions for bigger input   In 2   l      value    apple    blah   2     value    banana    blah   3      value    cars    blah  4     9000000 In 3   def gen version               for i in l                 yield i get  value   None          In 4   def list comp verison               return  i get  value   None  for i in l          In 5   def list verison               ll                 for i in l                 ll append i get  value   None              return ll In 10   def map lambda version                 m   map lambda i i get  value   None   l               return m          In 11    timeit gen version   172 ns    0 393 ns per loop  mean    std  dev  of 7 runs  10000000 loops each  In 12    timeit map lambda version   203 ns    2 31 ns per loop  mean    std  dev  of 7 runs  1000000 loops each  In 13    timeit list comp verison   1 61 s    20 4 ms per loop  mean    std  dev  of 7 runs  1 loop each  In 14    timeit list verison   2 29 s    4 58 ms per loop  mean    std  dev  of 7 runs  1 loop each    As you can see  generators are a better solution in comparison to the others  map is also slower compared to generator for reason I will leave up to OP to figure out

[python] Getting a list of values from a list of dicts

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