Tagged Questions

0
votes
0answers
33 views

R Quadratic programming and constrained optimization problem [closed]

I want find a vector p which lies in the positive null space of a matrix S and as well minimize the value of a least squares function with respect to p. Constraints are thus that p>0 and S*p=0 Here is ...
2
votes
1answer
66 views

The sample size applied to a non-normal distribution

I have a single variable that represents my population values (sample of data): ...
3
votes
2answers
152 views

Cluster Big Data in R and Is Sampling Relevant?

I'm new to data science and have a problem finding clusters in a data set with 200,000 rows and 50 columns in R. Since the data have both numeric and nominal variables, methods like K-means which ...
1
vote
1answer
75 views

What is behind JAGS (Just Another Gibbs Sampler)?

I have been using JAGS but I am not quite sure how it actually simulates it values. I need to know in a general sense what's going on in the background. Thanks for the help
0
votes
1answer
106 views

R: Density estimation vs Histogram Estimation

To draw random samples from a custom distribution, I recall reading that KDE's are better than histograms. (See hadley's comment here.) When I experimented in R, I am finding that the KDE method ...
0
votes
0answers
36 views

How to pick a sample from a multiple group, stratified population for repeat surveys

I provide support to about 500 internal customers on a computer system. I want to start measuring my 'customers' satisfaction on some kind of routine schedule. However my customer base can be ...
1
vote
3answers
83 views

Downsampling excessively sampled curves

I'm looking for a quick (event if not so accurate) way to deal with over-sampled curves using R. Consider the following example in which x contains 1000 values in ...
0
votes
0answers
32 views

Condition in conditioned latin hypercube sampling

I am trying to use conditioned latin hypercube sampling in R (clhs package, see here). Unfortunately, I don't really understand how the cost parameter can be used. ...
4
votes
0answers
80 views

Regarding the sampling procedure in Adaboost algorithm

The AdaBoost algorithm states that it is to train a classifier based on the training data according to a weight vector. Assume the size of training data is N, the weight vector is of dimension N as ...
0
votes
1answer
37 views

Sampling method for constructing multiple groups from a given pool

There is a set A having $N$ elements. Based on set A, I would like to construct $M$ groups, where each group has $P$ elements. Naturally, $M P <N$. All of those elements in the $M$ groups are ...
1
vote
1answer
269 views

mtry and unbalanced use of predictor variables in Random Forest

I am working on the Random Forest prediction, with the focus on the importance of predictor variables, and have a question regarding understanding of mtry and the actual usage of variables in the ...
1
vote
2answers
71 views

Statistical test to find variable causing failure

I have a database with tests that are either a pass or fail and around 25 description fields. Each description field is either a boolean or has between 3 and 10 options. I'd like to hook into my ...
1
vote
1answer
187 views

What are the rules / guidelines for downsampling?

I have a data set with ~ 7 million rows, of which ~ 100k are positives. I'm looking to shrink the data by keeping all the ...
2
votes
1answer
105 views

Absent categorical data levels in Bootstrap samples

I have a huge dataset ($n$ around five million, $p$ around three thousand) for a classification problem, where my interest is predictive class probabilities for test data, not the target. I shall be ...
4
votes
2answers
167 views

How to reconstruct database from cross-tabulated data?

I am given a set of almost 100 crosstabulations (most 2D, but some three dimensional) based on a single, yet unavailable dataset. My task is to perform basic statistical tests ($\chi^2$, Mann-Whitney, ...
7
votes
3answers
930 views

How to resample in R without repeating permutations?

In R, if I set.seed(), and then use the sample function to randomize a list, can I guarantee I won't generate the same permutation? ie... ...
5
votes
2answers
798 views

How do I sample without replacement using a sampling-with-replacement function?

I vaguely recall from grad school that the following is a valid approach to do a weighted sampling without replacement: Start with an initially empty "sampled set". Draw a (single) weighted sample ...
2
votes
2answers
701 views

A robust R package to do MCMC and Gibbs sampling

I need to make linear model for which I need to do Gibbs sampling in MCMC simulations. The model needed to be fitted is a linear mixed model. Please suggest me for a robust R package for this task.
7
votes
1answer
673 views

How to calculate sample size for comparing the area under the curve of two models?

Because I would like to calculate the sample size for comparing the area under the curve (AUC) of 2 models (cross-sectional study, predictor = continuous variable). Can you point me which function in ...
3
votes
1answer
238 views

Incidence density sampling in R

I was wondering if there is an R package to perform incidence density sampling for a case-control design. That is, for matching in a case-control design; accounting for multiple matching covariates.
3
votes
1answer
1k views

Generating random samples from a custom distribution

I am trying to generate random samples from a custom pdf using R. My pdf is: $$f_{X}(x) = \frac{3}{2} (1-x^2), 0 \le x \le 1$$ I generated uniform samples and then tried to transform it to my custom ...
6
votes
3answers
428 views

Multistage sampling in R

I've got a dataset similar to this: ...
3
votes
1answer
191 views

Sample selection and variation in the variable of interest when using panel data

I wonder how to reason when selecting samples. I am doing a panel data regression analysis about how the euro membership correlates with the budget deficit in the member countriues. Using R that is: ...
3
votes
3answers
1k views

How to re-sample an XTS time series in R?

I have an irregularly spaced XTS time series (with POSIXct values as index type). How can I build a new time series sampled at ...
1
vote
2answers
381 views

Should I use an average ECDF?

This relates to a previous question of mine which didn't gain many responses, perhaps because it wasn't very clear nd well written. I hope this time I will be more accurate and get your much ...
10
votes
3answers
464 views

Estimate the size of a population being sampled by the number of repeat observations

Say I have a population of 50 million unique things, and I take 10 million samples (with replacement)... The first graph is I've attached shows how many times I sample the same "thing", which is ...