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Hi guys i have a dictionary that looks like this:
[[['Test', 0,1],['Test2', 0,4],['Test3', 0,5],['Test4', 0,2],['Test5', 0,6],...]]
How can I get the top two (for example)?
Expected result:
[['Test3', 0,5],['Test5',0,6]]
Sort by the third value:
>>> sorted(l[0], key=lambda x: x[2])[-2:]
[['Test3', 0, 5], ['Test5', 0, 6]]
test = [[['Test', 0,1],['Test2', 0,4],['Test3', 0,5],['Test4', 0,2],['Test5', 0,6]]]
result = sorted(test[0], key=lambda x: x[2])[-2:]
print(result)
Output:
[['Test3', 0, 5], ['Test5', 0, 6]]
Something like this?
(I am assuming that you actually mean ['Test', 0, 1] to be a list with 3 elements which is to be sorted by the third element rather than a two element list with the second element being a float, in which case it should be ['Test', 0.1] and you can look at #jonrsharpe's answer. I also assumed that the output order (lowest to highest) is relevant.)
That is not a dictionary, it is a list ([]) containing another list which contains lists. Each sub-sub-list contains three elements:
['Test2', 0, 4]
#^0 ^1 ^2
Note that Python doesn't allow the user of commas as decimal points; I think you want 0.4.
Assuming that, sorting the sub-list and extracting the two highest sub-sub-lists is easy:
from operator import itemgetter
output = sorted(lst[0], key=itemgetter(1), reverse=True)[:2]
If I am wrong about the comma, make the argument to itemgetter 2.
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For a homework assignment I am given this task:
Read a list of numbers and generate a new list which squares the members of the original list.
generate a third list of ints that ranks the second list of ints.
What does it mean to "rank the list"? What is this asking me to do?
I am NOT asking for a solution to the programming assignment, please do not provide one.
To create a list of integers between 0 and N, a solution is to use the range(N) function.
Then you can use the append() method which adds an item to the end of the list while getting the square of each element.
Finally use the sort() method which sorts the list ascending by default. You can also make a function to decide the sorting criteria(s)
def printSortedList():
l = list()
for i in range(1,21):
l.append(i**2)
l.sort()
print(l)
printSortedList()
Ranking means to number the items in a list from lowest to highest, or vice-versa.
So, for example, “ranking” the list [639, 810, 150, 162, 461, 853, 648] produces the list [4, 6, 1, 2, 3, 7, 5], where 1 corresponds to the lowest value (150), 2 to the next-lowest value (162).
Or maybe you're supposed to rank them the other way, giving [4, 2, 7, 6, 5, 1, 3].
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I have a list like this:
my_lst = [[1,2,3,4]]
I was wondering how can I remove [] from the list to get the following list:
my_lst = [1,2,3,4]
The double [[]] is because you have a list containing a list. To get out the inner list, just index it:
my_lst = my_lst[0]
or unpack it:
[my_lst] = my_lst
Unpacking has the mild advantage that it will give you an error if the outer list doesn't not contain exactly one value (while my_lst[0] will silently discard any extra values).
There are many other options.
my_lst = my_lst[0]
You have a list with one element, which is itself a list. You want the variable to just be that first element, the list 1,2,3,4.
you have a list of lists.
my_lst = my_lst[0] #get the first list of the list
You can use itertools to achieve that without writing your explicit loop if the length of the outer list could be more than one.
In [47]: import itertools
In [49]: list(itertools.chain.from_iterable([[1, 2, 3], [1, 2]]))
Out[49]: [1, 2, 3, 1, 2]
You can reduce 1 dimension using sum.
my_lst=sum(my_lst,[])
# [1,2,3,4]
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Say I've a list with a fixed size and elements.
I wish to create set of all possible combinations of the elements inside the array. How do I achieve this?
In python I've tried to use itertools like this:
import itertools
a = [4, 7]
for L in range(0, len(a)+1):
for subset in itertools.combinations(a, L):
print(subset)
Howsoever, this gives me an output(),(4),(7),(4,7) as in tuples. I want 4,7,47,74 as my desired output in a list or array(C++) and not to print them after each loop iteration.
I don't know if that's permutation or combination. So kindly bear with me and help.
From your sample output (which by the way is not in agreement with your input), it is clear that you don't need combinations but permutations from itertools. You can use join to merge your two numbers for printing purpose.
Most importantly, you should start your loop over L from 1 because you need at least length of 1 to generate the permutations other wise you will get empty lists (tuples) as you mentioned in your question.
import itertools
a = [4, 7]
lst = []
for L in range(1, len(a)+1):
for subset in itertools.permutations(a, L):
lst.append(''.join(str(x) for x in subset))
for l in lst:
print (l)
Output
4
7
47
74
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I'm currently trying to complete Computer Science Circles online but I am stuck on part 14: Methods. Here is the question.
Using index and other list methods, write a function replace(list, X, Y) which replaces all occurrences of X in list with Y. For example, if L = [3, 1, 4, 1, 5, 9] then replace(L, 1, 7) would change the contents of L to [3, 7, 4, 7, 5, 9]. To make this exercise a challenge, you are not allowed to use [].
Note: you don't need to use return.
I would probably be able to do this if we were allowed to use square brackets.
Here is what I have so far.
def replace(L, X, Y):
while X in L:
var = L.index(X)
var = Y
return(L)
I'll give some tips since this is an exercise.
1) You already found out the index where you're supposed to replace one element with another. What other way is there to replace a value in a given index? Check all the methods of list.
2) A list comprehension also allows an elegant solution:
[...???... for value in list]
You'll need to figure out what the expression should be, and how to make the comprehension modify your original list, not just create a new one.
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I have the following dictionary:
StudentGrades = {
'Ivan': [4.32, 3, 2],
'Martin': [3.45, 5, 6],
'Stoyan': [2, 5.67, 4],
'Vladimir': [5.63, 4.67, 6]
}
I want to make a function that prints the average of the grades of the students, i.e. the average of the values
This answer was intended for Python2, which is now dead
Okay, so let's iterate over all dictionary keys and average the items:
avgDict = {}
for k,v in StudentGrades.iteritems():
# v is the list of grades for student k
avgDict[k] = sum(v)/ float(len(v))
In Python3, the iteritems() method is no longer necessary, can use items() directly.
now you can just see :
avgDict
Out[5]:
{'Ivan': 3.106666666666667,
'Martin': 4.816666666666666,
'Stoyan': 3.89,
'Vladimir': 5.433333333333334}
From your question I think you're queasy about iteration over dicts, so here is the same with output as a list :
avgList = []
for k,v in StudentGrades.iteritems():
# v is the list of grades for student k
avgDict.append(sum(v)/ float(len(v)))
Be careful though : the order of items in a dictionary is NOT guaranteed; this is, the order of key/values when printing or iterating on the dictionary is not guaranteed (as dicts are "unsorted").
Looping over the same identical dictionary object(with no additions/removals) twice is guaranteed to behave identically though.
If you don't want to do the simple calculation use statistics.mean:
from statistics import mean
StudentGrades = {
'Ivan': [4.32, 3, 2],
'Martin': [3.45, 5, 6],
'Stoyan': [2, 5.67, 4],
'Vladimir': [5.63, 4.67, 6]
}
for st,vals in StudentGrades.items():
print("Average for {} is {}".format(st,mean(vals)))
from scipy import mean
map(lambda x: mean(StudentGrades[x]), StudentGrades)
Generates this output:
[3.1066666666666669,
3.8900000000000001,
5.4333333333333336,
4.8166666666666664]
If you prefer a non-scipy solution one could use sum and len like supposed by Jiby:
map(lambda x: sum(StudentGrades[x])/len(StudentGrades[x]), StudentGrades)
EDIT: I am terribly sorry, I forgot you want a Python 3.4 solution, therefore (because you would get a map object returned) you need, for example, an additional list command:
from scipy import mean
list(map(lambda x: mean(StudentGrades[x]), StudentGrades))
This will return the desired output.