How to find all minimum elements in a list of tuples?

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How can I find all the minimum elements in a list? Right now I have a list of tuples, i.e.


So I want the output which is all the minimum elements of the list, in a new list. For example


I tried

minimumBy (comparing fst) xs

but that only returns the first minimum element.

After you obtain the minimum of the first value, we can filter the list on these items. Because you here want to retrieve a list of minimum items, we can cover the empty list as well by returning an empty list:

minimumsFst :: Ord a => [(a, b)] -> [(a, b)]
minimumsFst [] = []
minimumsFst xs = filter ((==) minfst . fst) xs
    where minfst = minimum (map fst xs)

For example:

Prelude> minimumsFst [(10,'a'),(5,'b'),(1,'c'),(8,'d'),(1,'e')]

Python, The computation of min and max value is a quite common utility in any programming domain be it functions to perform the task of getting the minimum and maximum value of a particular element position. to get min and max in list of tuples. result = list(filter(lambda x: x.count(1) > 0, a)) which searches the tuples in list for any occurrence of 1. If the search is limited to the first element, the solution can be modified into: result = list(filter(lambda x: x[0] == 1, a)) share. Share a link to this answer. Copy link. |.

Oneliner. The key is sorting.

Prelude Data.List> let a = [(1,'c'),(2,'b'),(1,'w')]
Prelude Data.List> (\xs@((m,_):_) -> takeWhile ((== m) . fst ) xs) . sortOn fst $ a

Python, Sometimes, while working with data in form of records, we can have a problem in which we need to find the minimum element of all the records received. This is  Python | Filter tuples according to list element presence Python - Rear element extraction from list of tuples records Python - Find the Maximum of Similar Indices in two list of Tuples

Here's a solution that works in one pass (most other answers here do two passes: one to find the minimum value and one to filter on it), and doesn't rely on how the sorting functions are implemented to be efficient.

{-# LANGUAGE ScopedTypeVariables #-}

import Data.Foldable (foldl')

minimumsBy :: forall a. (a -> a -> Ordering) -> [a] -> [a]
minimumsBy _ [] = []
minimumsBy f (x:xs) = postprocess $ foldl' go (x, id) xs
    go :: (a, [a] -> [a]) -> a -> (a, [a] -> [a])
    go acc@(x, xs) y = case f x y of
      LT -> acc
      EQ -> (x, xs . (y:))
      GT -> (y, id)
    postprocess :: (a, [a] -> [a]) -> [a]
    postprocess (x, xs) = x:xs []

Note that the [a] -> [a] type I'm using here is called a difference list, aka a Hughes list.

How to use Python's min() and max() with nested lists –, Let's talk about using Python's min and max functions on a list containing other Finding the minimum or maximum element of a list of lists based on a specific Maybe sometimes it'll be the third or fourth item, or a different kind of lookup is necessary all together. The code in this tutorial will work fine on a list of tuples. ↩. Python List: Exercise - 60 with Solution. Write a Python program to find a tuple, the smallest second index value from a list of tuples. Sample Solution:- Python Code: x = [(4, 1), (1, 2), (6, 0)] print(min(x, key=lambda n: (n[1], -n[0]))) Sample Output: (6, 0) Pictorial Presentation: Flowchart: Visualize Python code execution:

You tried

minimumBy (comparing fst) xs

which can also be written as

= head . sortBy (comparing fst) $ xs
= head . sortOn fst $ xs
= head . head . group . sortOn fst $ xs
= head . head . groupBy ((==) `on` fst) . sortOn fst $ xs

This returns just the first element instead of the list of them, so just drop that extra head to get what you want:

=        head . groupBy ((==) `on` fst) . sortOn fst $ xs

Of course having head is no good since it'll error out on the [] input. Instead, we can use the safe option,

= concat . take 1 . groupBy ((==) `on` fst) . sortOn fst $ xs

By the way any solution that calls minimum is also unsafe for the empty input list:

> head []
*** Exception: Prelude.head: empty list

> minimum []
*** Exception: Prelude.minimum: empty list

but takeWhile is safe:

> takeWhile undefined []

edit: thanks to laziness, the overall time complexity of the final version should still be O(n) even in the worst case.

Python: Find a tuple, the smallest second index value from a list of , Python: Find a tuple, the smallest second index value from a list of tuples a Python program to check if the n-th element exists in a given list. print ("The original list is : " + str(test_list)) # using min () and max () # to get min and max in list of tuples. res1 = min(test_list) [0], max(test_list) [0] res2 = min(test_list) [1], max(test_list) [1] # printing result.

You can do it easily too with foldr:

minimumsFst :: Ord a => [(a, b)] -> [(a, b)]
minimumsFst xs = go (minfst xs) xs
  go mn ls = foldr (\(x, y) rs -> if (x ==  mn) then (x,y) : rs else rs) [] xs
  minfst ls = minimum (map fst ls)

with your example:

   minimumsFst [(10,'a'),(5,'b'),(1,'c'),(8,'d'),(1,'e')]
=> [(1,'c'),(1,'e')]

Python Data Type: List - Exercises, Practice, Solution, Write a Python program to sum all the items in a list. a Python program to find a tuple, the smallest second index value from a list of tuples. >>> py_tuple = (1,2,3,4) >>> #to find the maximum and the minimum item from the tuple >>> max(py_tuple) #this will return 4 4 >>> min(py_tuple) #this will return 1 1. So, this all about Python tuples and different functional operations related to tuples.

Python : min() function Tutorial with examples –, Python provides a min() function to find out the smallest element from a Using min() function with an Iterable like list or tuple etc. Find If there are multiple min elements then we need a customized solution to find all the min  If you’re searching for a fully matching tuple among a list of tuples, you could simply use the in operator to implicitly call the list type’s __contains__() special method. If (1,2) in [(0,1),(2,3),(1,2),]: pass If you’re looking for some match inside one of the nested tuples, then you’d iterate over the calls to in

Lists and tuples, More generally, the right side can be any kind of sequence (string, list or tuple). max and min are built-in functions that find the largest and smallest elements of  The list is the first mutable data type you have encountered. Once a list has been created, elements can be added, deleted, shifted, and moved around at will. Python provides a wide range of ways to modify lists. Modifying a Single List Value. A single value in a list can be replaced by indexing and simple assignment: >>>

Tuples, But if you try to modify one of the elements of the tuple, you get an error: More generally, the right side can be any kind of sequence (string, list or tuple). Related Posts: Python Tuple: Different ways to create a tuple and Iterate over it; Python : How to find an element in Tuple by value; Python: How to sort a list of tuples by 2nd Item using Lambda Function or Comparator

  • You calculate the minimum, and then you filter the list.
  • Sorting takes O(n lg n) time, which is significantly slower than O(n) achieved by the minimum/filter combination.
  • @chepner you're forgetting about the laziness. :)
  • How does laziness guarantee that sortOn can produce the minimum value(s) in o(n lg n) time? (Although, I can probably answer my own question if a spend more than two seconds thinking about which sorting algorithm is used...)
  • @chepner that used to be a hot topic. take k . sort is O(n) (for small ks) when sort is lazy (on-line), like mergesort. When the first (minimal) element is found, only O(n) comparisons have been made, and the rest of tree of comparisons is yet to be explored. so it's O(k*n) for take n, and for a small fixed k it's O(n).
  • @chepner (correction: for take k). but here the k isn't fixed, you ask? well, if k was large, that means we had nearly-sorted input and the sort itself was O(n).
  • Is there a good reference for this fact, aside from linking to the implementation?
  • it should be under "k largest" or something.
  • It's also a little disturbing that Data.OldList appears to have the option to use insertion sort for sortBy (based the value of USE_REPORT_PRELUDE), although there doesn't seem to be any mention of sorting in the Haskell report (1998 or 2010).
  • very impressive answer
  • I would expect this to cause minfst xs to be recomputed at each step, which is needlessly expensive. I'd rather remove the argument, and use ... where minfst = minimum (map fst xs).
  • in any case this is reimplementation of filter, and minimum . map fst is reimplementation of fst . minimumBy (comparing fst).
  • if you're already re-implementing stuff with foldr, you could go one extra step and fuse the finding of the minimum in, as well. one foldr to do the whole job. :)