Questions tagged [sampling]
In signal processing, sampling is the reduction of a continuous signal to a discrete signal. In statistics, sampling is the selection of a subset of individuals from within a statistical population to estimate characteristics of the whole population.
sampling
151
questions
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Stratified random sampling from data frame
I have a data frame in the format:
head(subset)
# ants 0 1 1 0 1
# age 1 2 2 1 3
# lc 1 1 0 1 0
I need to create new data frame with random samples according to age and lc. For example I want ...
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93
votes
13
answers
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Take n random elements from a List<E>?
How can I take n random elements from an ArrayList<E>? Ideally, I'd like to be able to make successive calls to the take() method to get another x elements, without replacement.
user568866
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votes
1
answer
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How to draw waveform of Android's music player? [closed]
one of the default live wallpapers that came with my phone was a wallpaper that displayed the wave form of music playing in the background in real time. I was wondering how one could go about doing ...
5
votes
2
answers
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How do I double the size of a vector in MATLAB with interpolation?
Essentially, if I have the following matrix:
[1, 2, 3 ,4, 10]
I need to explode it whilst interpolating, as follows:
[1, 1.5, 2, 2.5, 3, 3.5, 4, 7, 10].
Essentially, buff it up by filling in the ...
- 8,269
3
votes
1
answer
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Looping at a constant rate with high precision for signal sampling
I am trying to sample a signal at 10Khz in Python. There is no problem when try to run this code(at 1KHz):
import sched, time
i = 0
def f(): # sampling function
s.enter(0.001, 1, f, ())
...
- 331
48
votes
5
answers
108k
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Random Sample of a subset of a dataframe in Pandas
I have a pandas DataFrame with 100,000 rows and want to split it into 100 sections with 1000 rows in each of them.
How do I draw a random sample of certain size (e.g. 50 rows) of just one of the 100 ...
- 738
6
votes
1
answer
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Efficient algorithm for generating unique (non-repeating) random numbers
I want to solve the following problem. I have to sample among an extremely large set, of the order of 10^20 and extracting a sample without repetitions of size about 10%-20%. Given the size of the set,...
40
votes
1
answer
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What are chunks, samples and frames when using pyaudio
After going through the documentation of pyaudio and reading some other articles on the web, I am confused if my understanding is correct.
This is the code for audio recording found on pyaudio's site:...
- 2,543
19
votes
1
answer
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sample random point in triangle [closed]
Suppose you have an arbitrary triangle with vertices A, B, and C. This paper (section 4.2) says that you can generate a random point, P, uniformly from within triangle ABC by the following convex ...
- 13k
14
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4
answers
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Random sampling to give an exact sum
I want to sample 140 numbers between 1000 to 100000 such that the sum of these 140 numbers is around 2 million (2000000):
sample(1000:100000,140)
such that:
sum(sample(1000:100000,140)) = 2000000
...
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4
votes
5
answers
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drawing a stratified sample in R
Designing my stratified sample
library(survey)
design <- svydesign(id=~1,strata=~Category, data=billa, fpc=~fpc)
So far so good, but how can I draw now a sample in the same way I was able for ...
- 1,332
79
votes
2
answers
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What does replacement mean in numpy.random.choice?
Here explains the function numpy.random.choice. However, I am confused about the third parameter replace. What is it? And in which case will it be useful? Thanks!
- 1,343
14
votes
8
answers
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OpenCV, how to use arrays of points for smoothing and sampling contours?
I have a problem to get my head around smoothing and sampling contours in OpenCV (C++ API).
Lets say I have got sequence of points retrieved from cv::findContours (for instance applied on this this ...
- 2,240
13
votes
1
answer
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Taking a disproportionate sample from a dataset in R
If I have a large dataset in R, how can I take random sample of the data taking into consideration the distribution of the original data, particularly if the data are skewed and only 1% belong to a ...
- 221
13
votes
4
answers
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Stratified splitting of pandas dataframe into training, validation and test set
The following extremely simplified DataFrame represents a much larger DataFrame containing medical diagnoses:
medicalData = pd.DataFrame({'diagnosis':['positive','positive','negative','negative','...
- 9,263
7
votes
1
answer
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How to repeat 1000 times this random walk simulation in R?
I'm simulating a one-dimensional and symmetric random walk procedure:
y[t] = y[t-1] + epsilon[t]
where white noise is denoted by epsilon[t] ~ N(0,1) in time period t. There is no drift in this ...
- 491
6
votes
2
answers
2k
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Randomly selecting values from an existing matrix after adding a vector (in R)
Thank you so much for your help in advance!
I am trying to modify an existing matrix such that, when a new line is added to the matrix, it removes values from the preexisting matrix.
For example, I ...
- 689
2
votes
2
answers
1k
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accurate sampling in c++
I want to sample values I get from a gpio 4000 times per second, currently I do something like that:
std::vector<int> sample_a_chunk(unsigned int rate, unsigned int block_size_in_seconds) {
...
- 1,799
2
votes
1
answer
3k
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How to get sound data sample value in c#
I need to get the sample values of sound data of a WAV file so that by using those sample values i need to get the amplitude values of that sound data in every second.
Important: Is there any way to ...
- 103
58
votes
8
answers
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Algorithms for determining the key of an audio sample
I am interested in determining the musical key of an audio sample. How would (or could) an algorithm go about trying to approximate the key of a musical audio sample?
Antares Autotune and Melodyne ...
- 4,884
12
votes
4
answers
7k
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Oversampling functionality in Tensorflow dataset API
I would like to ask if current API of datasets allows for implementation of oversampling algorithm? I deal with highly imbalanced class problem. I was thinking that it would be nice to oversample ...
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8
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1
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Pandas: Sampling from a DataFrame according to a target distribution
I have a Pandas DataFrame containing a dataset D of instances drawn from a distribution x. x may be a uniform for example.
Now, I want to draw n samples from D, sampled according to some new ...
- 975
7
votes
2
answers
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Why set.seed() affects sample() in R
I always thought set.seed() only makes random variable generators (e.g., rnorm) to generate a unique sequence for any specific set of input values.
However, I'm wondering, why when we set the set.seed(...
- 7,457
6
votes
2
answers
3k
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AudioRecord object not initializing in a project
When I am trying to record an audio through my Nexus 5 using following code
record = new AudioRecord(MediaRecorder.AudioSource.MIC, sampleRate, AudioFormat.CHANNEL_IN_MONO, AudioFormat....
- 1,469
6
votes
6
answers
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How do I call CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer?
I'm trying to figure out how to call this AVFoundation function in Swift. I've spent a ton of time fiddling with declarations and syntax, and got this far. The compiler is mostly happy, but I'm left ...
- 61.7k
6
votes
2
answers
4k
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Simulate samples from a joint cumulative distribution function?
I have a joint density function for two independent variables X and Y. And I now want to sample new x,y from this distribution.
What I believe I have to do is to find the joint cumulative ...
- 14.1k
5
votes
5
answers
1k
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Sample with a max
If I want to sample numbers to create a vector I do:
set.seed(123)
x <- sample(1:100,200, replace = TRUE)
sum(x)
# [1] 10228
What if I want to sample 20 random numbers that sum to 100, and then ...
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4
votes
2
answers
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Interpolation/subsampling of 3D data in python without VTK
What I want to do is rather simple but I havent found a straightforward approach thus far:
I have a 3D rectilinear grid with float values (therefore 3 coordinate axes -1D numpy arrays- for the ...
- 1,274
4
votes
1
answer
5k
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How to play a sound with a given sample rate in Java?
I was wondering if there is a library or something to play a sound on a given sample rate (20–20,000 Hz). Actually, I found something but I'm not understanding how I can make it work!
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4
votes
5
answers
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Sampling from a discrete probability distribution in C++
I am new to C++ and extremely surprised by the lack of accessible, common probability manipulation tools (i.e. the lack of things in Boost and the standard library). I've done a lot of scientific ...
- 76k
4
votes
2
answers
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Simplest way to capture raw audio from audio input for real time processing on a mac
What is the simplest way to capture audio from the built in audio input and be able to read the raw sampled values (as in a .wav) in real time as they come in when requested, like reading from a ...
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votes
1
answer
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Controlling sampling for crossvalidation in the caret R package
I have the following problem. In a data set from N subjects I have several samples per subject. I want to train a model on the data set, but I would like to make sure that in each resampling, in the ...
- 16.7k
3
votes
1
answer
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Change the playback rate of a track in real time on Android
I would like to know if somebody knows a library to changing the playback rate of a track in real time. My idea is to load a track and change its playback rate to half or double. Firstly, I tried with ...
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votes
2
answers
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Sampling small data frame from a big dataframe
I am trying to sample a data frame from a given data frame such that there are enough samples from each of the levels of a variable.
This can be achieved by separating the data frame by the levels and ...
- 5,160
2
votes
2
answers
4k
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Stratified sampling - not enough observations
What I would like to achieve is get a 10% sample from each group (which is a combination of 2 factors - recency and frequency category). So far I have thought about package sampling and function ...
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2
votes
1
answer
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MATLAB: Comparing 2 arrays with different lengths
I have two arrays with different lengths (due to different sampling rates) that I need to compare. I'd like to downsample the larger array to match the smaller one in length, however the factor is not ...
- 139
1
vote
2
answers
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CV and under sampling on a test fold
I am a bit lost on building a ML classifier with imbalanced data (80:20). The dataset has 30 columns; the target is Label.
I want to predict the major class.
I am trying to reproduce the following ...
- 231
1
vote
1
answer
2k
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Monte Carlo integration using importance sampling given a proposal function
Given a Laplace Distribution proposal:
g(x) = 1/2*e^(-|x|)
and sample size n = 1000, I want to Conduct the Monte Carlo (MC) integration for estimating θ:
via importance sampling. Eventually I want ...
- 75
1
vote
3
answers
6k
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Android SENSOR_DELAY_FASTEST isn't fast enough
I'm using the sensors to balance a robot, but SENSOR_DELAY_FASTEST only provides a 10Hz sampling rate, which is simply not fast enough. Is there a way of sampling even faster?
Is there a way of ...
- 13
1
vote
1
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Stratified sample when some strata are too small
I need to draw a stratified sample with n observation in each stratum, but some strata have fewer observations than n. If a stratum has too few observations (say, k<n observations), I want to ...
- 838
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votes
1
answer
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Update values of a matrix variable in tensorflow, advanced indexing
I would like to create a function that for every line of a given data X, is applying the softmax function only for some sampled classes, lets say 2, out of K total classes. In simple python the code ...
- 241
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votes
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answers
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How to generate a random 4 digit number not starting with 0 and having unique digits?
This works almost fine but the number starts with 0 sometimes:
import random
numbers = random.sample(range(10), 4)
print(''.join(map(str, numbers)))
I've found a lot of examples but none of them ...
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17
votes
2
answers
7k
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Is there an algorithm for weighted reservoir sampling? [closed]
Is there an algorithm for how to perform reservoir sampling when the points in the data stream have associated weights?
- 601
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votes
5
answers
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Random Sampling from Mongo
I have a mongo collection with documents. There is one field in every document which is 0 OR 1. I need to random sample 1000 records from the database and count the number of documents who have that ...
- 832
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votes
6
answers
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How to keep a random subset of a stream of data?
I have a stream of events flowing through my servers. It is not feasible for me to store all of them, but I would like to periodically be able to process some of them in aggregate. So, I want to ...
- 17.1k
14
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1
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Efficiently picking a random element from a chained hash table?
Just for practice (and not as a homework assignment) I have been trying to solve this problem (CLRS, 3rd edition, exercise 11.2-6):
Suppose we have stored n keys in a hash table of size m, with
...
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6
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Select cells randomly from NumPy array - without replacement
I'm writing some modelling routines in NumPy that need to select cells randomly from a NumPy array and do some processing on them. All cells must be selected without replacement (as in, once a cell ...
- 28.1k
13
votes
4
answers
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Profiling a (possibly I/O-bound) process to reduce latency
I want to improve the performance of a specific method inside a larger application.
The goal is improving latency (wall-clock time spent in a specific function), not (neccessarily) system load.
...
- 6,808
11
votes
2
answers
8k
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Profilers Instrumenting Vs Sampling
I am doing a study to between profilers mainly instrumenting and sampling.
I have came up with the following info:
sampling: stop the execution of program, take PC and thus deduce were the program is
...
- 6,092
10
votes
2
answers
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Android: startRecording() called on an uninitialized AudioRecord when SAMPLERATE set to 44100
I get an error, when I set the sampling rate to 44100 for the AudioRecord object. When it's 22050 it works fine.
02-16 10:45:45.099 24021-24021/com.vlad.jackcomms E/AudioRecord﹕ frameCount 1024 < ...
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