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How is “int* ptr = int()” value initialization not illegal?
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110
int() is a constant expression with a value of 0, so it's a valid way of producing a null pointe...
pandas: filter rows of DataFrame with operator chaining
... boolean index.
In [96]: df
Out[96]:
A B C D
a 1 4 9 1
b 4 5 0 2
c 5 5 1 0
d 1 3 9 6
In [99]: df[(df.A == 1) & (df.D == 6)]
Out[99]:
A B C D
d 1 3 9 6
If you want to chain methods, you can add your own mask method and use that one.
In [90]: def mask(df, key, ...
Find XOR of all numbers in a given range
...ven a large range [a,b] where 'a' and 'b' can be typically between 1 and 4,000,000,000 inclusive. You have to find out the XOR of all the numbers in the given range.
...
Share Large, Read-Only Numpy Array Between Multiprocessing Processes
I have a 60GB SciPy Array (Matrix) I must share between 5+ multiprocessing Process objects. I've seen numpy-sharedmem and read this discussion on the SciPy list. There seem to be two approaches-- numpy-sharedmem and using a multiprocessing.RawArray() and mapping NumPy dtype s to ctype s. ...
How do I make an html link look like a button?
...
answered Apr 2 '09 at 15:06
TStamperTStamper
28.2k1010 gold badges6161 silver badges7272 bronze badges
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How to form tuple column from two columns in Pandas
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208
Get comfortable with zip. It comes in handy when dealing with column data.
df['new_col'] = li...
What does this square bracket and parenthesis bracket notation mean [first1,last1)?
...rst1 (and includes it), but ends just before last1.
Assuming integers:
(0, 5) = 1, 2, 3, 4
(0, 5] = 1, 2, 3, 4, 5
[0, 5) = 0, 1, 2, 3, 4
[0, 5] = 0, 1, 2, 3, 4, 5
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...
Designing function f(f(n)) == -n
...w about:
f(n) = sign(n) - (-1)n * n
In Python:
def f(n):
if n == 0: return 0
if n >= 0:
if n % 2 == 1:
return n + 1
else:
return -1 * (n - 1)
else:
if n % 2 == 1:
return n - 1
else:
return -1 * (n ...
CSS: bolding some text without changing its container's size
...h a little compromise, I used text-shadow instead.
li:hover {text-shadow:0px 0px 1px black;}
Here's a working example:
body {
font-family: segoe ui;
}
ul li {
display: inline-block;
border-left: 1px solid silver;
padding: 5px
}
.textshadow :hover {
text-shadow: 0px 0p...
What's the fastest way to merge/join data.frames in R?
...he first example sqldf is 3x slower than data.table and in the second its 200x faster than plyr and 100 times faster than data.table. Below we show the input code, the output timings for the merge and the output timings for the aggregate. Its also worthwhile noting that sqldf is based on a databa...