R-lda | Latent Dirichlet allocation package for R | Topic Modeling library
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Latent Dirichlet allocation package for R
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QUESTION
I am wondering which technique is used to learn the Dirichlet priors in Mallet's LDA implementation.
Chapter 2 of Hanna Wallach's Ph.D. thesis gives a great overview and a valuable evaluation of existing and new techniques to learn the Dirichlet priors from the data.
Tom Minka initially provided his famous fixed-point iteration approach, however without any evaluation or recommendations.
Furthermore, Jonathan Chuang did some comparisons between previously proposed methods, including the Newton−Raphson method.
LiangJie Hong says the following in his blog:
A typical approach is to utilize Monte-Carlo EM approach where E-step is approximated by Gibbs sampling while M-step is to perform a gradient-based optimization approach to optimize Dirichlet parameters. Such approach is implemented in Mallet package.
Mallet mentions the Minka's fixed-point iterations with and without histograms.
However, the method that is actually used simply states:
Learn Dirichlet parameters using frequency histograms
Could someone provide any reference that describes the used technique?
...ANSWER
Answered 2021-May-21 at 13:47It uses the fixed point iteration. The frequency histograms method is just an efficient way to calculate it. They provide an algebraically equivalent way to do the exact same computation. The update function consists of a sum over a large number of Digamma functions. This function by itself is difficult to compute, but the difference between two Digamma functions (where the arguments differ by an integer) is relatively easy to compute, and even better, it "telescopes" so that the answer to Digamma(a + n) - Digamma(a) is one operation away from the answer to Digamma(a + n + 1) - Digamma(a). If you work through the histogram of counts from 1 to the max, adding up the number of times you saw a count of n at each step, the calculation becomes extremely fast. Initially, we were worried that hyperparameter optimization would take so long that no one would do it. With this trick it's so fast it's not really significant compared to the Gibbs sampling.
QUESTION
I cannot longer open my test plan that I worked on yesterday. I get the following error message: "Unexpected error - see log for details".
I've tried to apply the solution proposed here: jmeter error on opening script but I had no luck finding the line that caused the problem.
Do I have to completely redo this test?
Here is the log file:
jmeter.log
...ANSWER
Answered 2018-Mar-12 at 08:55HTTPSampler2
was removed as a part of Bug 60727 so you won't be able to use it with JMeter 3.3.
If you really need this plugin you will have to downgrade to JMeter 3.1, it can be downloaded from JMeter Archives page.
QUESTION
Following up on Keep csv feature labels for LDA pca I decided to ignore feature names for my PCA reduction. I am using pandas read_csv() function and would like to ignore string/text columns, which happen to be every odd-numbered column. So either a filter to remove string columns or odd-number columns when reading in my csv would be helpful
...ANSWER
Answered 2018-Dec-10 at 00:26One way is to read column labels and then take every second column via the usecols
parameter of pd.read_csv
. This assumes your column labels are unique, but will be efficient as you are not reading expensive object
dtype series.
QUESTION
I am currently working on a PySpark job (Spark 2.2.0) which intends to train a Latent Dirichlet Allocation model based on a set of documents. Input documents are provided as a CSV file located on Google Cloud Storage.
The following code successfully ran on a single node Google Cloud Dataproc cluster (4vCPUs / 15GB of memory) with a small subset of documents (~6500), a low number of topics to generate (10) and a low number of iterations (100). However, other attempts with a larger set of documents or higher values for either the number of topics or number of iterations quickly led to memory issues and job failures.
Also, when submitting this job to a 4 nodes cluster, I could see that only one worker node was actually working (30% CPU usage), letting me think that the code is not properly optimized for parallel processing.
Code ...ANSWER
Answered 2017-Aug-26 at 01:29If your input data size is small even if your pipeline ends up doing dense computation on the small data, then size-based partitioning will lead to too few partitions for scalability. Since your getNumPartitions()
prints 1
, this indicates that Spark will use at most 1 executor core to process that data, which is why you're only seeing one worker node working.
You can try changing your initial spark.read.csv
line to include a repartition
at the end:
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