``init``
--------
- Available in: GLRM, K-means
- Hyperparameter: yes
Description
~~~~~~~~~~~
This option specifies the initialization mode used in K-Means. The options are Random, Furthest, PlusPlus, and User.
- **Random**: Choose :math:`K` clusters from the set of :math:`N` observations at random so that each observation has an equal chance of being chosen.
- **Furthest** (Default):
a. Choose one center :math:`m_{1}` at random.
b. Calculate the difference between :math:`m_{1}` and each of the remaining :math:`N-1` observations :math:`x_{i}`. :math:`d(x_{i}, m_{1}) = ||(x_{i}-m_{1})||^2`
c. Choose :math:`m_{2}` to be the :math:`x_{i}` that maximizes :math:`d(x_{i}, m_{1})`.
d. Repeat until :math:`K` centers have been chosen.
- **PlusPlus**:
a. Choose one center :math:`m_{1}` at random.
b. Calculate the difference between :math:`m_{1}` and each of the remaining :math:`N-1` observations :math:`x_{i}`. :math:`d(x_{i}, m_{1}) = \|(x_{i}-m_{1})\|^2`
c. Let :math:`P(i)` be the probability of choosing :math:`x_{i}` as :math:`m_{2}`. Weight :math:`P(i)` by :math:`d(x_{i}, m_{1})` so that those :math:`x_{i}` furthest from :math:`m_{2}` have a higher probability of being selected than those :math:`x_{i}` close to :math:`m_{1}`.
d. Choose the next center :math:`m_{2}` by drawing at random according to the weighted probability distribution.
e. Repeat until :math:`K` centers have been chosen.
- **User** initialization allows you to specify a file (using the ``user_points`` parameter) that includes a vector of initial cluster centers.
**Notes**:
- The user-specified points dataset must have the same number of columns as the training observations.
- This option is ignored when ``estimate_k`` is enabled. In this case, the algorithm is deterministic.
- If this option is not specified but a user-points file is specified, then this value will default to ``user``.
Related Parameters
~~~~~~~~~~~~~~~~~~
- `estimate_k `__
- `user_points `__
Example
~~~~~~~
.. example-code::
.. code-block:: r
library(h2o)
h2o.init()
# import the seeds dataset:
# this dataset looks at three different types of wheat varieties
# the original dataset can be found at http://archive.ics.uci.edu/ml/datasets/seeds
seeds <- h2o.importFile("https://s3.amazonaws.com/h2o-public-test-data/smalldata/flow_examples/seeds_dataset.txt")
# set the predictor names
# ignore the 8th column which has the prior known clusters for this dataset
predictors <-colnames(seeds)[-length(seeds)]
# split into train and validation
seeds_splits <- h2o.splitFrame(data = seeds, ratios = .8, seed = 1234)
train <- seeds_splits[[1]]
valid <- seeds_splits[[2]]
# try using the `init` parameter:
# build the model with three clusters
seeds_kmeans <- h2o.kmeans(x = predictors, k = 3, init='Furthest', training_frame = train, validation_frame = valid, seed = 1234)
# print the total within cluster sum-of-square error for the validation dataset
print(paste0("Total sum-of-square error for valid dataset: ", h2o.tot_withinss(object = seeds_kmeans, valid = T)))
# select the values for `init` to grid over:
# Note: this dataset is too small to see significant differences between these options
# the purpose of the example is to show how to use grid search with `init` if desired
hyper_params <- list( init = c("PlusPlus", "Furthest", "Random") )
# this example uses cartesian grid search because the search space is small
# and we want to see the performance of all models. For a larger search space use
# random grid search instead: list(strategy = "RandomDiscrete")
grid <- h2o.grid(x = predictors, k = 3, training_frame = train, validation_frame = valid,
algorithm = "kmeans", grid_id = "seeds_grid", hyper_params = hyper_params,
search_criteria = list(strategy = "Cartesian"), seed = 1234)
## Sort the grid models by TotSS
sortedGrid <- h2o.getGrid("seeds_grid", sort_by = "tot_withinss", decreasing = F)
sortedGrid
.. code-block:: python
import h2o
from h2o.estimators.kmeans import H2OKMeansEstimator
h2o.init()
# import the seeds dataset:
# this dataset looks at three different types of wheat varieties
# the original dataset can be found at http://archive.ics.uci.edu/ml/datasets/seeds
seeds = h2o.import_file("https://s3.amazonaws.com/h2o-public-test-data/smalldata/flow_examples/seeds_dataset.txt")
# set the predictor names
# ignore the 8th column which has the prior known clusters for this dataset
predictors = seeds.columns[0:7]
# split into train and validation sets
train, valid = seeds.split_frame(ratios = [.8], seed = 1234)
# try using the `init` parameter:
# initialize the estimator then train the model
seeds_kmeans = H2OKMeansEstimator(k = 3, init='Furthest', seed = 1234)
seeds_kmeans.train(x = predictors, training_frame = train, validation_frame= valid)
# print the total within cluster sum-of-square error for the validation dataset
print("sum-of-square error for valid:",seeds_kmeans.tot_withinss(valid = True))
# grid over `init`
# import Grid Search
from h2o.grid.grid_search import H2OGridSearch
# select the values for `init` to grid over
# Note: this dataset is too small to see significant differences between these options
# the purpose of the example is to show how to use grid search with `init` if desired
hyper_params = {'init': ["PlusPlus", "Furthest", "Random"]}
# this example uses cartesian grid search because the search space is small
# and we want to see the performance of all models. For a larger search space use
# random grid search instead: {'strategy': "RandomDiscrete"}
# initialize the estimator
seeds_kmeans = H2OKMeansEstimator(k = 3, seed = 1234)
# build grid search with previously made Kmeans and hyperparameters
grid = H2OGridSearch(model = seeds_kmeans, hyper_params = hyper_params,
search_criteria = {'strategy': "Cartesian"})
# train using the grid
grid.train(x = predictors, training_frame = train, validation_frame = valid)
# sort the grid models by total within cluster sum-of-square error.
sorted_grid = grid.get_grid(sort_by='tot_withinss', decreasing= False)
print(sorted_grid)