Python: Converting Pseudo-code to code

Question

I tried coding these lines:

copy the first {ceiling of} n/2 points of P to array Pleft
copy the same {ceiling of} n/2 points from Q to array Qleft
copy the remaining {floor of} n/2 points of P to array Pright
copy the same {floor of} n/2 points from Q to array Qright 
m = P[ ({ceiling of} n/2) - 1].x

And I got:

mid = len(P) / 2

Pl = P[:mid]
Ql = Q[:mid]
Pr = P[mid:]
Qr = Q[mid:]
m = P[:mid - 1].x

But I do not know how to code this line:

copy all the points of array Q for which |x - m| < d into new array S[0..num - 1]

Please help.

You need math.abs() and list comprehensions (or a simple for-loop) for this. — Michael Butscher
– Michael Butscher, Commented Nov 14, 2017 at 2:23
By the way: You overwrite mid without using it. It can only hold one value. — Michael Butscher
– Michael Butscher, Commented Nov 14, 2017 at 2:25

PaSTE · Accepted Answer · 2017-11-19 05:34:38Z

1

EDIT: Oops! Forgot that m is a list!

This is what list comprehensions are for. Because m is a list, you'll also need to make use of python's zip function. The definition of the new array is:

S = [x for x, y in zip(Q, m) if abs(x - y) < d]

You'll have to supply d. Also, for completeness:

num = len(S)

edited Nov 19, 2017 at 5:34

answered Nov 14, 2017 at 2:28

PaSTE

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2 Comments

Heart Killer Over a year ago

But there's this error for this code: "TypeError: unsupported operand type(s) for -: 'tuple' and 'tuple'"

PaSTE Over a year ago

I can't tell what the structure of Q or m from the code you posted, so I assumed they were simple lists of numeric types. By the text of the error, it appears to be a list of tuples. You will either have to post how Q and P are constructed in your question, or modify the code I posted to put the tuple indices on x and y in the call abs(x - y).

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