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Find MongoDB records where array field is not empty
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answered Aug 5 '14 at 15:24
Chris'Chris'
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Are list-comprehensions and functional functions faster than “for loops”?
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154
The following are rough guidelines and educated guesses based on experience. You should timeit ...
pandas: filter rows of DataFrame with operator chaining
...the 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, ke...
[A]System.Web.WebPages.Razor.Configuration.HostSection cannot be cast to… web.config issue
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I am using VS2013, MVC 5.2.2.0, Web Api 2. I have just changed the all versions from 2.0.0.0 to 3.0.0.0 of the following section of Web.config resides inside the View folder of my project.
<configSections>
<sectionGroup name="system.web.w...
Why does (0 < 5 < 3) return true?
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Order of operations causes (0 < 5 < 3) to be interpreted in javascript as ((0 < 5) < 3) which produces (true < 3) and true is counted as 1, causing it to return true.
This is also why (0 < 5 < 1) returns false, (0 < 5) returns true, wh...
How to define a two-dimensional array?
...tems; Python calls this
"list comprehension".
# Creates a list containing 5 lists, each of 8 items, all set to 0
w, h = 8, 5;
Matrix = [[0 for x in range(w)] for y in range(h)]
You can now add items to the list:
Matrix[0][0] = 1
Matrix[6][0] = 3 # error! range...
Matrix[0][6] = 3 # valid
Not...
How do you rotate a two dimensional array?
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Here it is in C#
int[,] array = new int[4,4] {
{ 1,2,3,4 },
{ 5,6,7,8 },
{ 9,0,1,2 },
{ 3,4,5,6 }
};
int[,] rotated = RotateMatrix(array, 4);
static int[,] RotateMatrix(int[,] matrix, int n) {
int[,] ret = new int[n, n];
for (int i = 0; i < n; ++i) {
for (i...
How do I calculate percentiles with python/numpy?
...ile() is available in numpy too.
import numpy as np
a = np.array([1,2,3,4,5])
p = np.percentile(a, 50) # return 50th percentile, e.g median.
print p
3.0
This ticket leads me to believe they won't be integrating percentile() into numpy anytime soon.
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Logical operators for boolean indexing in Pandas
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unutbuunutbu
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Find indices of elements equal to zero in a NumPy array
...numpy.where() is my favorite.
>>> x = numpy.array([1,0,2,0,3,0,4,5,6,7,8])
>>> numpy.where(x == 0)[0]
array([1, 3, 5])
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