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I have an assignment to generate the following lists using only basic python functions (no numpy). Here is all of my code:

#1.Create a list which contains i^2 with i = 1 through 5
squares = [pow(i,2) for i in range(1,6)]
#print squares

#2. Create a list which contains log[j] with j = 1 through 5
logs = map(math.log10,range(1,6))
#print logs

#3. Create a list which contains [i_1*j_1, i_2*j_2, i_3,j_3...]
def mult(x,y): return x*y
lmultl = map(mult,squares,logs)
#print lmultl

#4 Create a list which contains [[i_1*j_1, i_1*j_2, i_1*j_3...][i_2*j_1, i_2*j_2, i_2*j_3...]etc]
logslol = [[logs]*5] #Returns a list of lists with 5 copies of list "logs"
def lrep(x): return [x,x,x,x,x] #Returns a list w/ 5 copies of each integer 
squareslol= map(lrep,squares) #Returns list of lists "for squares"

print map(mult,logslol,squareslol) #Attempt 1 to create goal list
print [logslol*item for item in squareslol] #Attempt 2 to create goal list

My Question is for the final print statements in list #4: I am getting a TypeError: "can't multiply sequence by non-int of type 'list'" for both methods. Is there a more efficient way to multiply each element in two "list of lists"?

Griggs Hutaff
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2 Answers2

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Try this approach:

results = []
for i,j in zip(squares,logs)
     x = i*j
     results.append(x)
Monica
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  • Or even `results = list(map(lambda x: x[0]*x[1], zip(squares, logs)))` – ForceBru Aug 10 '16 at 20:35
  • Both suggestions above are appropriate for multiplying elements in the "squares" and "logs" lists; however, when multiplying elements in the "squareslol" and "logslol" lists (which are "list of lists") both suggestions still return the same TypeError as my original code. – Griggs Hutaff Aug 10 '16 at 20:52
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import math
squares = [pow(i,2) for i in range(1,6)]
logs = map(math.log10,range(1,6))

mult = lambda x,y: x*y 
lmultl = map(mult,squares,logs)

I assume for you elements in squares are i_1, i_2, i_3... and elements in logs are j_1, j_2, j_3...

And you want to create a list multiplying each element of squares with each element of logs which contains [[i_1*j_1, i_1*j_2, i_1*j_3...] [i_2*j_1, i_2*j_2, i_2*j_3...] etc], then use the below code :-

sqr_mul_log = [[m*n for m in logs ] for n in squares]

For the reverse sequence i.e. multiplying each element of logs with each element of squares which contains [[j_1*i_1, j_1*i_2, j_1*i_3...] [j_2*i_1, j_2*i_2, j_2*i_3...] etc], then use the below code :-

log_mul_sqr = [[m*n for m in squares] for n in logs]

Also, this will remove the overhead of creating squareslol and logslol that you are creating at #4

Pabitra Pati
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  • Thank you. I suspected that the `squareslol` and `logslol` were unnecessary. Showing the reverse sequence was especially helpful in understanding how the command is interpreted. – Griggs Hutaff Aug 25 '16 at 19:43
  • Initially it was difficult for me to understand what you are willing to do at step 4. I just saw the example of [i_1*j_1, i_1*j_2, ..], [i_2*j_1, i_2*j_2,...], etc...] and wrote the solution. – Pabitra Pati Aug 26 '16 at 00:38