How do I raise list element in dict value to power of x?

Question

I am a beginner in Python and have several exercises to resolve.

One of these is:

"Define a dictionary w/ keys "abc", "xyz" and values [1, 2, 3] and [9, 10, 11]; iterate over all values (lists) and raise to the power of 4 each element of each list and print to screen"

...and I am bit lost. I could define a function that raises the power of each element in a list, but I do not know how to do it in a dictionary :(

This is where I am stuck:

dex = {"abc":[1,2,3],"xyz":[9,10,11]}
for x in dex.values():
     print(x)

Where exactly are you stuck? you said you know how to do it for a list. `x` in your code is a list — DeepSpace, Apr 07 '22 at 12:45
@DeepSpace thanks for the clue so I just had to loop the elements in the list again I guess. I didn't know I could have a For inisde another For but I appreciate the teaching by questioning :) — Catalin Agarbiceanu, Apr 07 '22 at 12:56

score 0 · Answer 1 · answered Apr 07 '22 at 12:49

0

Since it's nested you could use a loop in a loop to get each item of each list, like this:

dex = {"abc":[1,2,3],"xyz":[9,10,11]}
for x in dex.values():
     for el in x:
         print(el**4)

or using dict and list comprehension:

dex = {"abc":[1,2,3],"xyz":[9,10,11]}
dex = {k: [el**4 for el in v] for k, v in dex.items()}
print(dex)

answered Apr 07 '22 at 12:49

David

173
12

I didn't know I could have another for loop in my existing one sorry I am very new and it is all very confusing/ Thank you! – Catalin Agarbiceanu Apr 07 '22 at 12:54
@CatalinAgarbiceanu Welcome, you can have as many nested loop or if conditions as you wish :) – David Apr 07 '22 at 12:56

score 0 · Answer 2 · answered Apr 07 '22 at 12:51

0

This way should work, if you can use dict comprehensions. It uses map, which applies a function to each elem in a list.

my_dict = {"abc": [1, 2, 3], "xyz": [9, 10, 11]}
new_dict = {key: list(map(lambda x: x ** 4, val)) for key, val in my_dict.items()}

Here, we map a function that raises each item in the list to a power.

answered Apr 07 '22 at 12:51

Anonymous

452
2
9

Why do you use map/lambda instead of list comprehension. Does it have advantages or just another way of doing it? – David Apr 07 '22 at 12:58
1

@David imo it’s a bit easier to see what’s happening. I dont think theres any major performance difference, no, but they do the same thing. – Anonymous Apr 07 '22 at 17:05

score 0 · Answer 3 · answered Apr 07 '22 at 12:53

0

Depending on how you want to present the output, this might work for you:

dex = {"abc": [1,2,3], "xyz": [9,10,11]}
print([[e**4 for e in lst] for lst in dex.values()])

Output:

[[1, 16, 81], [6561, 10000, 14641]]

answered Apr 07 '22 at 12:53

DarkKnight

19,739
3
6
22

score 0 · Answer 4 · answered Apr 07 '22 at 12:56

This should work :

dex = {"abc":[1,2,3],"xyz":[9,10,11]}

def print_exp (dic) :
    for i,j in dic.items() :
        if isinstance(j,list):
            for n in j :
                print(n**4)
            
print_exp(dex)

This one is with a function definition.

Without function definition you can achieve this by :

dex = {"abc":[1,2,3],"xyz":[9,10,11]}


for i,j in dex.items() :
    if isinstance(j,list):
        for n in j :
            print(n**4)

score 0 · Answer 5 · answered Apr 07 '22 at 14:24

Since the index (or the power) stays constant, the magic method __rpow__ can be used to chain the operations: a**4 <--> int.__pow__(a, 4) <--> int.__rpow__(4, a)

dex = {"abc":[1,2,3],"xyz":[9,10,11]}

pows = [list(map(int(4).__rpow__, l)) for l in dex.values()]

print(pows)

Output

[[1, 16, 81], [6561, 10000, 14641]]

How do I raise list element in dict value to power of x?

5 Answers5