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Cost of len() function
...
360
It's O(1) (constant time, not depending of actual length of the element - very fast) on every ...
Optional Parameters with C++ Macros
...S(message, size) PrintString(message, size, 0)
#define PRINT_STRING_3_ARGS(message, size, style) PrintString(message, size, style)
#define GET_4TH_ARG(arg1, arg2, arg3, arg4, ...) arg4
#define PRINT_STRING_MACRO_CHOOSER(...) \
GET_4TH_ARG(__VA_ARGS__, PRINT_STRING_3_ARGS, \
...
How do you get the magnitude of a vector in Numpy?
...ray -- say x.norm() -- but oh well).
import numpy as np
x = np.array([1,2,3,4,5])
np.linalg.norm(x)
You can also feed in an optional ord for the nth order norm you want. Say you wanted the 1-norm:
np.linalg.norm(x,ord=1)
And so on.
...
How do you know when to use fold-left and when to use fold-right?
... you use a left fold. Example (haskell-style pseudocode)
foldl (-) [1, 2, 3] == (1 - 2) - 3 == 1 - 2 - 3 // - is left-associative
If your operator is right-associative (right fold), the parentheses would be set like this:
A x (B x (C x D))
Example: Cons-Operator
foldr (:) [] [1, 2, 3] == 1 : ...
Is generator.next() visible in Python 3?
...
3 Answers
3
Active
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Python pandas Filtering out nan from a data selection of a column of strings
...NaN:
In [87]:
nms
Out[87]:
movie name rating
0 thg John 3
1 thg NaN 4
3 mol Graham NaN
4 lob NaN NaN
5 lob NaN NaN
[5 rows x 3 columns]
In [89]:
nms = nms.dropna(thresh=2)
In [90]:
nms[nms.name.notnull()]
Out[90]:
movie name rating
0...
Is there an R function for finding the index of an element in a vector?
... function match works on vectors :
x <- sample(1:10)
x
# [1] 4 5 9 3 8 1 6 10 7 2
match(c(4,8),x)
# [1] 1 5
match only returns the first encounter of a match, as you requested. It returns the position in the second argument of the values in the first argument.
For multiple matching, ...
Preserving signatures of decorated functions
...))
return f(*args, **kwargs)
@args_as_ints
def funny_function(x, y, z=3):
"""Computes x*y + 2*z"""
return x*y + 2*z
print funny_function("3", 4.0, z="5")
# 22
help(funny_function)
# Help on function funny_function in module __main__:
#
# funny_function(x, y, z=3)
# Computes x*y + ...
Small Haskell program compiled with GHC into huge binary
...
Let's see what's going on, try
$ du -hs A
13M A
$ file A
A: ELF 64-bit LSB executable, x86-64, version 1 (SYSV),
dynamically linked (uses shared libs), for GNU/Linux 2.6.27, not stripped
$ ldd A
linux-vdso.so.1 => (0x00007fff1b9ff000)
libXr...
Base64: What is the worst possible increase in space usage?
...the size of the base-64 representation of a string of size n is:
ceil(n / 3) * 4
So, for a 16kB array, the base-64 representation will be ceil(16*1024/3)*4 = 21848 bytes long ~= 21.8kB.
A rough approximation would be that the size of the data is increased to 4/3 of the original.
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