i'm using weka to do some text mining, i'm a little bit confused so i'm here to ask how can i ( with a set of comments that are in a some way classified as: notes, status of work, not conformity, warning) predict if a new comment belong to a specific class, with all the comment (9551) i've done a preprocess obtaining with the filter "stringtowordvector" a vector of tokens, and then i've used the simple kmeans to obtain a number of cluster.
So the question is: if a user post a new comment can i predict with those data if it belong to a category of comment?
sorry if my question is a little bit confused but so am i.
thank you
Trivial Training-validation-test
Create two datasets from your labelled instances. One will be training set and the other will be validation set. The training set will contain about 60% of the labelled data and the validation will contain 40% of the labelled data. There is no hard and fast rule for this split, but a 60-40 split is a good choice.
Use K-means (or any other clustering algorithm) on your training data. Develop a model. Record the model's error on training set. If the error is low and acceptable, you are fine. Save the model.
For now, your validation set will be your test dataset. Apply the model you saved on your validation set. Record the error. What is the difference between training error and validation error? If they both are low, the model's generalization is "seemingly" good.
Prepare a test dataset where you have all the features of your training and test dataset but the class/cluster is unknown.
Apply the model on the test data.
10-fold cross validation
Use all of your labelled data instances for this task.
Apply K-means (or any other algorithm of your choice) with a 10-fold CV setup.
Record the training error and CV error. Are they low? Is the difference between the errors is low? If yes, then save the model and apply it on the test data whose class/cluster is unknown.
NB: The training/test/validation errors and their differences will give you an "very initial" idea of overfitting/underfitting of your model. They are sanity tests. You need to perform other tests like learning curves to see if your model overfits or underfits or perfect. If there appears to be an overfitting and underfitting problem, you need to try many different techniques to overcome them.
Related
I have two datasets regarding whether a sentence contains a mention of a drug adverse event or not, both the training and test set have only two fields the text and the labels{Adverse Event, No Adverse Event} I have used weka with the stringtoWordVector filter to build a model using Random Forest on the training set.
I want to test the model built with removing the class labels from the test data set, applying the StringToWordVector filter on it and testing the model with it. When I try to do that it gives me the error saying training and test set not compatible probably because the filter identifies a different set of attributes for the test dataset. How do I fix this and output the predictions for the test set.
The easiest way to do this for a one off test is not to pre-filter the training set, but to use Weka's FilteredClassifier and configure it with the StringToWordVector filter, and your chosen classifier to do the classification. This is explained well in this video from the More Data Mining with Weka online course.
For a more general solution, if you want to build the model once then evaluate it on different test sets in future, you need to use InputMappedClassifier:
Wrapper classifier that addresses incompatible training and test data
by building a mapping between the training data that a classifier has
been built with and the incoming test instances' structure. Model
attributes that are not found in the incoming instances receive
missing values, so do incoming nominal attribute values that the
classifier has not seen before. A new classifier can be trained or an
existing one loaded from a file.
Weka requires a label even for the test data. It uses the labels or „ground truth“ of the test data to compare the result of the model against it and measure the model performance. How would you tell whether a model is performing well, if you don‘t know whether its predictions are right or wrong. Thus, the test data needs to have the very same structure as the training data in WEKA, including the labels. No worries, the labels are not used to help the model with its predictions.
The best way to go is to select cross validation (e.g. 10 fold cross validation) which automatically will split your data into 10 parts, using 9 for training and the remaining 1 for testing. This procedure is repeated 10 times so that each of the 10 parts has once been used as test data. The final performance verdict will be an average of all 10 rounds. Cross validation gives you a quite realistic estimate of the model performance on new, unseen data.
What you were trying to do, namely using the exact same data for training and testing is a bad idea, because the measured performance you end up with is way too optimistic. This means, you‘ll get very impressive figures like 98% accuracy during testing - but as soon as you use the model against new unseen data your accuracy might drop to a much worse level.
After I have trained a model, how do I use it with C++?
I have tried MXNet incubator-mxnet/example/image-classification/predict-cpp/
and incubator-mxnet/cpp-package/example/.
As part of training you should periodically evaluate your model against a validation set, at the end of each epoch for example. You should then have a good idea of the expected accuracy of the model when using the model to score new data, to determine if the model is really performing worse than expected at inference time.
If the validation accuracy of the model while training the model is no better than random (i.e. 1/number of classes), there could be many reasons for this including; poor model selection, incorrect loss calculation, wrong optimization technique and hyperparameters (e.g. learning rate).
If the test accuracy of the model on unseen data is poor, you might be trying to apply the model to a different domain to which it was trained. You can't use a model trained on handwritten characters (e.g. MNIST) to classify real world objects (e.g. ImageNet).
If you need a C++ example of model training, take a look at this tutorial.
I am classifying iris data using DECISION TREE (C4.5), RANDOM FOREST and NAIVE BAYES. I am using the dataset downloaded from iris-train and iris-test. When I train the all networks everything is fine with proper results with 'classifier output', 'Detailed accuracy with class' and 'confusion matrix'. But, when I select the iris-test data in the Weka-explorer-classify-test options and select the iris-test file and in 'more options' select 'output prediction' as 'csv' and click start, I am getting the result as shown in the figure below. The 'classifier output' is showing the classified samples correctly, but, 'Detailed accuracy with class' and 'confusion matrix' is with all values zeros. Any suggestion where I am going wrong in selecting any option. Thank you.
The confusion matrix shows you how well your trained classifier performs by comparing the actual class of the instances in the test set with the class that was predicted by the classifier. But you are supplying a test set with no class information, so there's nothing to compare against. This is why you see
Total Number of Instances 0
Ignored Class Unknown Instances 120
in the output in your screenshot.
Typically you would first evaluate the performance of your classifier using cross-validation, or a test set that has class information. Then you can use the trained classifier to classify unknown data, for example using the Re-evaluate model on current test set right-click option as described in the help.
Say I have one batch that I want to train my model on. Do I simply run tf.Session()'s sess.run(batch) once, or do I have to iterate through all of the batch's examples with a loop in the session? I'm looking for the optimal way to iterate/update the training ops, such as loss. I thought tensorflow would handle it itself, especially in the cases where tf.nn.dynamic_rnn() takes in a batch dimension for listing the examples. I thought, perhaps naively, that a for loop in the python code would be the inefficient method of updating the loss. I am using tf.losses.mean_squared_error(batch) for a regression problem.
My regression problem is given two lists of word vectors (300d each), and determines the similarity between the two lists on a continuous scale from [0, 5]. My supervised model is Deepmind's Differential Neural Computer (DNC). The problem is I do not believe it is learning anything. this is due to the fact that the all of the output from the model is centered around 0 and even negative. I do not know how it could possibly be negative given no negative labels provided. I only call sess.run(loss) for the single batch, I do not create a python loop to iterate through it.
So, what is the most efficient way to iterate the training of a model and how do people go about it? Do they really use python loops to do multiple calls to sess.run(loss) (this was done in the training file example for DNC, and I have seen it in other examples as well). I am certain I get the final loss from the below process, but I am uncertain if the model has actually been trained entirely just because the loss was processed in one go. I also do not understand the point of update_ops returned by some functions, and am uncertain if they are necessary to ensure the model has been trained.
Example of what I mean by processing a batch's loss once:
# assume the model has been defined prior through batch_output_logits
train_loss = tf.losses.mean_squared_error(labels=target,
predictions=batch_output_logits)
with tf.Session() as sess:
sess.run(init_op) # pseudo code, unnecessary for question
coord = tf.train.Coordinator()
threads = tf.train.start_queue_runners(coord=coord)
# is this the entire batch's loss && model has been trained for that batch?
loss_np = sess.run(train_step, train_loss)
coord.request_stop()
coord.join(threads)
Any input on why I am receiving negative values when the labels are in the range [0, 5] is welcomed as well(general abstract answers for this are fine, because its not the main focus). I am thinking of attempting to create a piece-wise function, if possible, for my loss, so that for any values out of bounds face a rapidly growing exponential loss function. Uncertain how to implement, or if it would even work.
Code is currently private. Once allowed, I will make the repo public.
To run DNC model, go to the project/ directory and run python -m src.main. If there are errors you encounter feel free to let me know.
This model depends upon Tensorflow r1.2, most recent Sonnet, and NLTK's punkt for Tokenizing sentences in sts_handler.py and tests/*.
In a regression model, the network calculates the model output based on the randomly initialized values for your model parameters. That's why you're seeing negative values here; you haven't trained your model enough for it to learn that your values are only between 0 and 5.
Unless I'm missing something, you are only calculating the loss, but you aren't actually training the model. You should probably be calling sess.run(optimizer) on an optimizer, not on your loss function.
You probably need to train your model for multiple epochs (training your model for one epoch = training your model once on the entire dataset).
Batches are used because it is more computationally efficient to train your model on a batch than it is to train it on a single example. However, your data seems to be small enough that you won't have that problem. As such, I would recommend reducing your batch size to as low as possible. As a general rule, you get better training from a smaller batch size, at the cost of added computation.
If you post all of your code, I can take a look.
I am relatively new to the data mining area and have been experimenting with Weka.
I have a dataset which consists of almost 8000 records related to customers and items they have purchased. 58% of this data set has missing values for the "Gender" attribute.
I want to find the missing gender values based on the other data I do have.
I first thought I could do this using a classifier algorithm in Weka using a training set to build a model. Based on examples I saw online, I tried this with pretty much all the available algorithms available in Weka using a training set that consisted of 60-80% of the data which did not have missing values. This gave me a lower accuracy rate than I wanted (80-86% depending on the algorithm used)
Did I go about this correctly? Is there a way to improve this accuracy? I experimented with using different attributes, different pre-processing of the data etc.
I also tried using the ReplaceMissingValues filter on the complete dataset to see how that would handle the missing values. However, it just changed all the missing values to "Female" which obviously cannot be the case. So I'm wondering also wondering if I need to use this filter in my situation or not.
It sounds like you went about it in the correct way. The ReplaceMissingValues filter replaces the missing values with the most frequent of the non-missing values I think, so it is not what you want in this case.
A better way to get an idea of the true accuracy of your gender-predictor would be to use cross-validation instead of the training/test split (Weka has a separate option for that). 80-86% may seem low, but keep in mind that random guessing will only get you about 50%, so it's still a lot better than that. To try to get better performance, pick a classifier that performs well and then play with its parameters until you get better performance. This is likely to be quite labour-intensive (although you could of course use automated methods for tuning, see e.g. Auto-WEKA), but the only way to improve the performance.
You can also combine the algorithm you choose with a separate feature selection step (Weka has a special meta-classifier for this). This may improve performance, but again you'll have to experiment to find the particular configuration that works for you.