I have a list of tuples:
countries = [('Netherlands','31'),
('US','1'),
('Brazil','55'),
('Russia','7')]
Now, I want to find the index of the list, based on the first item in the tuple.
I have tried countries.index('Brazil'), I would like the output to be 2. But instead, that returns a ValueError:
ValueError: 'Brazil' is not in list
I am aware that I could convert this list into a pd DataFrame and then search for a pattern match within the first column. However, I suspect there is a faster way to do this.
You can use enumerate() to find your index:
Try:
idx = next(i for i, (v, *_) in enumerate(countries) if v == "Brazil")
print(idx)
Prints:
2
Related
Provided with a list of lists. Here's an example myList =[[70,83,90],[19,25,30]], return a list of lists which contains the difference between the elements. An example of the result would be[[13,7],[6,5]]. The absolute value of (70-83), (83-90), (19-25), and (25-30) is what is returned. I'm not sure how to iterate through the list to subtract adjacent elements without already knowing the length of the list. So far I have just separated the list of lists into two separate lists.
list_one = myList[0]
list_two = myList[1]
Please let me know what you would recommend, thank you!
A custom generator can return two adjacent items at a time from a sequence without knowing the length:
def two(sequence):
i = iter(sequence)
a = next(i)
for b in i:
yield a,b
a = b
original = [[70,83,90],[19,25,30]]
result = [[abs(a-b) for a,b in two(sequence)]
for sequence in original]
print(result)
[[13, 7], [6, 5]]
Well, for each list, you can simply get its number of elements like this:
res = []
for my_list in list_of_lists:
res.append([])
for i in range(len(my_list) - 1):
# Do some stuff
You can then add the results you want to res[-1].
List of integer value passed through input function and then stored in a list. After which performing the operation to find the sum of all the numbers in the list
lst = list( input("Enter the list of items :") )
sum_element = 0
for i in lst:
sum_element = sum_element+int(i)
print(sum_element)
Say you want to create a list with 8 elements. By writing list(8) you do not create a list with 8 elements, instead you create the list that has the number 8 as it's only element. So you just get [8].
list() is not a Constructor (like what you might expect from other languages) but rather a 'Converter'. And list('382') will convert this string to the following list: ['3','8','2'].
So to get the input list you might want to do something like this:
my_list = []
for i in range(int(input('Length: '))):
my_list.append(int(input(f'Element {i}: ')))
and then continue with your code for summation.
A more pythonic way would be
my_list = [int(input(f'Element {i}: '))
for i in range(int(input('Length: ')))]
For adding all the elements up you could use the inbuilt sum() function:
my_list_sum = sum(my_list)
lst=map(int,input("Enter the elements with space between them: ").split())
print(sum(lst))
I want to match two lists from which one list is smaller while other is a bigger one. If a match occurs between two lists then put the matching element in a new list at the same index instead of putting it another index. You can understand my question from the code given below:
list1=['AF','KN','JN','NJ']
list2=['KNJ','NJK','JNJ','INS','AFG']
matchlist = []
smaller_list_len = min(len(list1),len(list2))
for ind in range(smaller_list_len):
elem2 = list1[ind]
elem1 = list2[ind][0:2]
if elem1 in list2:
matchlist.append(list1[ind])
Obtained output
>>> matchlist
['KNJ', 'NJK', 'JNJ']
Desired Output
>>> matchlist
['AFG', 'KNJ', 'JNJ', 'NJK']
Is there a way to get the desired output?
Use a nested loop iterating over the 3-char list. When an item in that list contains the current item in the 2-char list, append it and break out of the inner loop:
list1=['AF','KN','JN','NJ']
list2=['KNJ','NJK','JNJ','INS','AFG']
matchlist = []
smaller_list_len = min(len(list1),len(list2))
for ind in range(smaller_list_len):
for item in list2:
if list1[ind] in item:
matchlist.append(item)
break
Given the question doesn't specify any constraints, in a more pythonic way, using a list comprehension:
list1=['AF','KN','JN','NJ']
list2=['KNJ','NJK','JNJ','INS','AFG']
matchlist=[e2 for e1 in list1 for e2 in list2 if e2.startswith(e1)]
produces
['AFG', 'KNJ', 'JNJ', 'NJK']
I was trying to scan an array for values and take action depending on the result. However, when I had a closer look at what the code was doing I noticed that my logical condition was ill posed.
I will illustrate what I mean with the following example:
#importing numpy
import numpy as np
#creating a test array
a = np.zeros((3,3))
#searching items bigger than 1 in 'a'
index = np.where(a > 1)
I was expecting my index to return an empty list. In fact it returns a tuple object, like:
index
Out[5]: (array([], dtype=int64), array([], dtype=int64))
So, the test I was imposing:
#testing if there are values
#in 'a' that fulfil the where condition
if index[0] != []:
print('Values found.')
#testing if there are no values
#in 'a' that fulfil the where condition
if index[0] == []:
print('No values found.')
Will not achieve its purpose because I was comparing different objects (is that correct to say?).
So what is the correct way to create this test?
Thanks for your time!
For your 2D array, np.where returns a tuple of arrays of indices (one for each axis), so that a[index] gives you an array of the elements fulfilling the condition.
Indeed, you compared an empty list to an empty array. Instead, I would compare the size property (or e.g. len()) of the first element of this tuple:
if index[0].size == 0:
print('No values found.')
Given this list of tuples:
my_tuples = [(1,2), (3,4)]
and the following evaluation function:
def evaluate(item_tuple):
return item_tuple[0] * 2
Question: how can I get the list item (tuple) that has the highest evaluation value? (I'm guessing I can use a list comprehension for this)
def max_item(tuples_list, evaluation_fn):
'''Should return the tuple that scores max using evaluation_fn'''
# TODO Implement
# This should pass
assertEqual((3,4), max_item(my_tuples, evaluate))
Correct me if I'm wrong, you want the list of tuples sorted by the result of multiplying one of the values inside the tuple with x (in your example above it would be the first value of the tuple multiplied by 2).
If so, you can do it this way:
from operator import itemgetter
sorted(l, key=itemgetter(0 * 2), reverse=True)
I managed to do it this way:
def max_item(tuples_list, evaluation_fn):
zipped = zip(map(evaluation_fn, tuples_list), tuples_list)
return max(zipped, key=lambda i:i[0])[1]
I don't know if there's a simpler (more pythonic?) way to solve it though.
Edit
I figured how I could use a list comprehension to make it more succinct/readable:
def max_item(tuples_list, evaluation_fn):
return max([(evaluation_fn(i), i) for i in tuples_list])[1]