Questions tagged [probability]
Consider if your question would be better at stats.stackexchange.com. Probability touches upon uncertainty, random phenomena, random numbers, random variables, probability distributions, sampling, combinatorics.
probability
4,062
questions
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Cosmic Rays: what is the probability they will affect a program?
Once again I was in a design review, and encountered the claim that the probability of a particular scenario was "less than the risk of cosmic rays" affecting the program, and it occurred to me that I ...
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494
votes
16
answers
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Find the similarity metric between two strings
How do I get the probability of a string being similar to another string in Python?
I want to get a decimal value like 0.9 (meaning 90%) etc. Preferably with standard Python and library.
e.g.
...
- 10.2k
308
votes
23
answers
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Generate a random point within a circle (uniformly)
I need to generate a uniformly random point within a circle of radius R.
I realize that by just picking a uniformly random angle in the interval [0 ... 2π), and uniformly random radius in the ...
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votes
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answer
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Minimizing NExpectation for a custom distribution in Mathematica
This relates to an earlier question from back in June:
Calculating expectation for a custom distribution in Mathematica
I have a custom mixed distribution defined using a second custom distribution ...
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votes
9
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Why is XOR the default way to combine hashes?
Say you have two hashes H(A) and H(B) and you want to combine them. I've read that a good way to combine two hashes is to XOR them, e.g. XOR( H(A), H(B) ).
The best explanation I've found is touched ...
- 3,921
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votes
4
answers
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Data structures for loaded dice?
Suppose that I have an n-sided loaded die, where each side k has some probability pk of coming up when I roll it. I’m curious if there is a good data structure for storing this information statically (...
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votes
3
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Why does this random value have a 25/75 distribution instead of 50/50?
Edit: So basically what I'm trying to write is a 1 bit hash for double.
I want to map a double to true or false with a 50/50 chance. For that I wrote code that picks some random numbers (just as an ...
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7
answers
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Is it safe to assume a GUID will always be unique?
I know there is a minute possibility of a clash but if I generated a batch of 1000 GUIDs (for example), would it be safe to assume they're all unique to save testing each one?
Bonus question
An ...
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votes
10
answers
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How to calculate probability in a normal distribution given mean & standard deviation?
How to calculate probability in normal distribution given mean, std in Python? I can always explicitly code my own function according to the definition like the OP in this question did: Calculating ...
- 20.4k
79
votes
14
answers
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Select k random elements from a list whose elements have weights
Selecting without any weights (equal probabilities) is beautifully described here.
I was wondering if there is a way to convert this approach to a weighted one.
I am also interested in other ...
- 10.2k
76
votes
13
answers
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How to pick an item by its probability?
I have a list of items. Each of these items has its own probability.
Can anyone suggest an algorithm to pick an item based on its probability?
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3
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Probability of SHA1 collisions
Given a set of 100 different strings of equal length, how can you quantify the probability that a SHA1 digest collision for the strings is unlikely... ?
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votes
3
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How do Markov Chain Chatbots work?
I was thinking of creating a chatbot using something like markov chains, but I'm not entirely sure how to get it to work. From what I understand, you create a table from data with a given word and ...
- 9,084
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votes
15
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What is the probability that the array will remain the same?
This question has been asked in Microsoft interview. Very much curious to know why these people ask so strange questions on probability?
Given a rand(N), a random generator which generates random ...
- 9,936
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votes
10
answers
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Multivariate normal density in Python?
Is there any python package that allows the efficient computation of the PDF (probability density function) of a multivariate normal distribution?
It doesn't seem to be included in Numpy/Scipy, and ...
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68
votes
11
answers
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Random number with Probabilities
I am wondering what would be the best way (e.g. in Java) to generate random numbers within a particular range where each number has a certain probability to occur or not?
e.g.
Generate random ...
- 5,846
62
votes
11
answers
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Normalizing a list of numbers in Python
I need to normalize a list of values to fit in a probability distribution, i.e. between 0.0 and 1.0.
I understand how to normalize, but was curious if Python had a function to automate this.
I'd ...
- 7,613
57
votes
2
answers
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Probability of collision when using a 32-bit hash
I have a 10-character string key field in a database. I've used CRC32 to hash this field, but I'm worrying about duplicates. Could somebody show me the probability of collision in this situation?
P.S.:...
- 1,211
54
votes
7
answers
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How to calculate mean, median, mode and range from a set of numbers
Are there any functions (as part of a math library) which will calculate mean, median, mode and range from a set of numbers.
- 12.8k
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votes
7
answers
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Generate Random Boolean Probability
I only know how I can generate a random boolean value (true/false).
The default probability is 50:50
But how can I generate a true false value with my own probability?
Let's say it returns true with ...
- 705
44
votes
5
answers
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Probability in Java
I was curious to know, how do I implement probability in Java? For example, if the chances of a variable showing is 1/25, then how would I implement that? Or any other probability? Please point me in ...
- 3,294
43
votes
2
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scikit-learn return value of LogisticRegression.predict_proba
What exactly does the LogisticRegression.predict_proba function return?
In my example I get a result like this:
array([
[4.65761066e-03, 9.95342389e-01],
[9.75851270e-01, 2.41487300e-02],
[...
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votes
4
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R: Calculate and interpret odds ratio in logistic regression
I am having trouble interpreting the results of a logistic regression. My outcome variable is Decision and is binary (0 or 1, not take or take a product, respectively).
My predictor variable is ...
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votes
6
answers
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How can I make a random choice according to probabilities stored in a list (weighted random distribution)?
Given a list of probabilities like:
P = [0.10, 0.25, 0.60, 0.05]
(I can ensure that the sum of all the variables in P is always 1)
How can I write a function that randomly returns a valid index, ...
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10
answers
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An interview question: About Probability
An interview question:
Given a function f(x) that 1/4 times returns 0, 3/4 times returns 1.
Write a function g(x) using f(x) that 1/2 times returns 0, 1/2 times returns 1.
My implementation is:
...
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36
votes
7
answers
53k
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How do I simulate flip of biased coin?
In unbiased coin flip H or T occurs 50% of times.
But I want to simulate coin which gives H with probability 'p' and T with probability '(1-p)'.
something like this:
def flip(p):
'''this ...
- 36.3k
36
votes
3
answers
52k
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How to get a classifier's confidence score for a prediction in sklearn?
I would like to get a confidence score of each of the predictions that it makes, showing on how sure the classifier is on its prediction that it is correct.
I want something like this:
How sure is ...
- 2,131
33
votes
6
answers
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How do I assess the hash collision probability?
I'm developing a back-end application for a search system. The search system copies files to a temporary directory and gives them random names. Then it passes the temporary files' names to my ...
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7
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How do I programmatically calculate Poker Odds? [closed]
I'm trying to write a simple game/utility to calculate poker odds. I know there's plenty of resources that talk about the formulas to do so, but I guess I'm having trouble translating that to code. ...
- 47.2k
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votes
5
answers
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What are probabilistic data structures?
I have read about "probabilistic" data structures like bloom filters and skip lists.
What are the common characteristics of probabilistic data structures and what are they used for?
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votes
7
answers
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Generate random integers with probabilities
I'm a bit confused about how to generate integer values with probabilities.
As an example, I have four integers with their probability values: 1|0.4, 2|0.3, 3|0.2, 4|0.1
How can I generate these ...
- 21.3k
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votes
2
answers
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Plotting probability density function by sample with matplotlib [closed]
I want to plot an approximation of probability density function based on
a sample that I have; The curve that mimics the histogram behaviour. I can
have samples as big as I want.
- 11.3k
30
votes
4
answers
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How to generate random numbers biased towards one value in a range?
Say, if I wanted to generate an unbiased random number between min and max, I'd do:
var rand = function(min, max) {
return Math.floor(Math.random() * (max - min + 1)) + min;
};
But what if I ...
- 21.7k
30
votes
8
answers
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Distributed probability random number generator
I want to generate a number based on a distributed probability. For example, just say there are the following occurrences of each numbers:
Number| Count
1 | 150
2 | ...
- 493
30
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9
answers
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How to do weighted random sample of categories in python
Given a list of tuples where each tuple consists of a probability and an item I'd like to sample an item according to its probability. For example, give the list [ (.3, 'a'), (.4, 'b'), (.3, 'c')] I'd ...
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Create Bayesian Network and learn parameters with Python3.x [closed]
I'm searching for the most appropriate tool for python3.x on Windows to create a Bayesian Network, learn its parameters from data and perform the inference.
The network structure I want to define ...
- 483
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votes
8
answers
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Random boolean with weight or bias
I need to generate some random booleans. However I need to be able to specify the probability of returning true. As a results doing:
private Random random = new Random();
random.nextBoolean();
will ...
- 2,040
28
votes
3
answers
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Defining a white noise process in Python
I need to draw samples from a white noise process in order to implement a particular integral numerically.
How do I generate this with Python (i.e., numpy, scipy, etc.)?
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6
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How much can you truncate a SHA1 hash and be reasonably sure of having an unique ID?
I am making an application that stores documents and gives each one a UID based on a SHA1 digest of a few things including the timestamp. The digest has a lot of characters, and I want to allow users ...
- 44.7k
27
votes
8
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Select random row from a PostgreSQL table with weighted row probabilities
Example input:
SELECT * FROM test;
id | percent
----+----------
1 | 50
2 | 35
3 | 15
(3 rows)
How would you write such query, that on average 50% of time i could get the row with id=...
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Why eigenvector & eigenvalue in LDA become zero?
I'd like to implement fast PLDA (Probabilistic Linear Discriminant Analysis) in OpenCV. in this, LINK fast PLDA have been implemented in Matlab and Python. One of the parts of PLDA is LDA. I've ...
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4
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Confidence interval for binomial data in R?
I know that I need mean and s.d to find the interval, however, what if the question is:
For a survey of 1,000 randomly chosen workers, 520 of them are female. Create a 95% confidence interval for the ...
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votes
7
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C puzzle: Make a fair coin from a biased coin
How can I determine the probability that a function would return 0 or 1 in the following case:
Let the function_A return 0 with
probability 40% and 1 with probability
60%. Generate a ...
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26
votes
8
answers
14k
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Game Design/theory, Loot Drop Chance/Spawn Rate
I have a very specific and long-winded question for you all. This question is both about programming and game-theory. I recently added spawnable ore to my Turn Based Strategy Game: http://imgur.com/...
- 4,274
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9
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What's the best way to unit test code that generates random output?
Specifically, I've got a method picks n items from a list in such a way that a% of them meet one criterion, and b% meet a second, and so on. A simplified example would be to pick 5 items where 50% ...
- 12k
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How do I calculate the probability for a given quantile in R?
Using R, it is trivial to calculate the quantiles for given probabilities in a sampled distribution:
x <- rnorm(1000, mean=4, sd=2)
quantile(x, .9) # results in 6.705755
However, I can't find an ...
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26
votes
3
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Fastest primality test
Could you suggest a fast, deterministic method that is usable in practice, for testing if a large number is prime or not?
Also, I would like to know how to use non-deterministic primality tests ...
user500944
25
votes
12
answers
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Python - Is a dictionary slow to find frequency of each character?
I am trying to find a frequency of each symbol in any given text using an algorithm of O(n) complexity. My algorithm looks like:
s = len(text)
P = 1.0/s
freqs = {}
for char in text:
try:
...
- 29.9k
25
votes
7
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Generate random number with given probability matlab
I want to generate a random number with a given probability but I'm not sure how to:
I need a number between 1 and 3
num = ceil(rand*3);
but I need different values to have different probabilities ...
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25
votes
1
answer
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Probability of hash collision
I am looking for some precise math on the likelihood of collisions for MD5, SHA1, and SHA256 based on the birthday paradox.
I am looking for something like a graph that says "If you have 10^8 ...
- 403