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Pandas aggregate count distinct
...>>> df.groupby("date").agg({"duration": np.sum, "user_id": lambda x: x.nunique()})
duration user_id
date
2013-04-01 65 2
2013-04-02 45 1
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Rails: select unique values from a column
...rks only on "top level" queries, like above. Doesn't work on collection proxies ("has_many" relations, for example).
Address.distinct.pluck(:city) # => ['Moscow']
user.addresses.distinct.pluck(:city) # => ['Moscow', 'Moscow', 'Moscow']
In this case, deduplicate after the query
user.address...
Python: using a recursive algorithm as a generator
...
def getPermutations(string, prefix=""):
if len(string) == 1:
yield prefix + string
else:
for i in xrange(len(string)):
for perm in getPermutations(string[:i] + string[i+1:], prefix+string[i]):
yield perm
...
Why is transposing a matrix of 512x512 much slower than transposing a matrix of 513x513?
After conducting some experiments on square matrices of different sizes, a pattern came up. Invariably, transposing a matrix of size 2^n is slower than transposing one of size 2^n+1 . For small values of n , the difference is not major.
...
Generating a random password in php
...s 1):
function randomPassword() {
$alphabet = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890';
$pass = array(); //remember to declare $pass as an array
$alphaLength = strlen($alphabet) - 1; //put the length -1 in cache
for ($i = 0; $i < 8; $i++) {
$n = ra...
Combining two lists and removing duplicates, without removing duplicates in original list
...econd list has any duplicates of the first list ignored. .. A bit hard to explain, so let me show an example of what the code looks like, and what i want as a result.
...
Convert pem key to ssh-rsa format
...eygen):
-m key_format Specify a key format for the -i (import) or -e (export) conversion options. The supported key formats are: “RFC4716” (RFC 4716/SSH2 public or private key), “PKCS8” (PEM PKCS8 public key) or “PEM” (PEM public key). The default conversion format is “RFC4716”...
Is there a difference between authentication and authorization?
...enticated) user should have to resources controlled by the system. For an example that may or may not be related to a web-based scenario, a database management system might be designed so as to provide certain specified individuals with the ability to retrieve information from a database but not the...
EF Code First: How do I see 'EntityValidationErrors' property from the nuget package console?
...
I got annoyed by this recently too. I fixed it by putting a wrapper function in the Configuration class in the Seed method, and replaced calls to SaveChanges with calls to my function instead. This function would simply enumerate the errors within the EntityValida...
Java integer to byte array
...putInt(1695609641).array();
for (byte b : bytes) {
System.out.format("0x%x ", b);
}
output:
0x65 0x10 0xf3 0x29
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