``col_sample_rate_per_tree``
----------------------------

- Available in: GBM, DRF, XGBoost, Isolation Forest, Uplift DRF
- Hyperparameter: yes

Description
~~~~~~~~~~~

This option specifies the column sampling rate for each tree (without replacement). This can be a value from 0.0 to 1.0 and defaults to 1. Note that it is multiplicative with ``col_sample_rate``, so setting both parameters to 0.8, for example, results in 64% of columns being considered at any given node to split.

For an example model using:
 
  - 100-column dataset
  - ``col_sample_rate_per_tree=0.754``
  - ``col_sample_rate=0.8`` (Samples 80% of columns per split)

For each tree, the floor is used to determine the number of columns - in this example, (0.754 * 100)=75 out of 100 - that are randomly picked, and then the floor is used to determine the number of columns - in this case, (0.754 * 0.8 * 100)=60 - that are then randomly chosen for each split decision (out of the 75).

Related Parameters
~~~~~~~~~~~~~~~~~~

- `col_sample_rate <col_sample_rate.html>`__
- `col_sample_rate_change_per_level <col_sample_rate_change_per_level.html>`__


Example
~~~~~~~

.. tabs::
   .. code-tab:: r R

		library(h2o)
		h2o.init()
		# import the airlines dataset:
		# This dataset is used to classify whether a flight will be delayed 'YES' or not "NO"
		# original data can be found at http://www.transtats.bts.gov/
		airlines <-  h2o.importFile("http://s3.amazonaws.com/h2o-public-test-data/smalldata/airlines/allyears2k_headers.zip")

		# convert columns to factors
		airlines["Year"] <- as.factor(airlines["Year"])
		airlines["Month"] <- as.factor(airlines["Month"])
		airlines["DayOfWeek"] <- as.factor(airlines["DayOfWeek"])
		airlines["Cancelled"] <- as.factor(airlines["Cancelled"])
		airlines['FlightNum'] <- as.factor(airlines['FlightNum'])

		# set the predictor names and the response column name
		predictors <- c("Origin", "Dest", "Year", "UniqueCarrier", "DayOfWeek", "Month", "Distance", "FlightNum")
		response <- "IsDepDelayed"

		# split into train and validation
		airlines_splits <- h2o.splitFrame(data =  airlines, ratios = 0.8, seed = 1234)
		train <- airlines_splits[[1]]
		valid <- airlines_splits[[2]]

		# try using the `col_sample_rate_per_tree` parameter:
		airlines_gbm <- h2o.gbm(x = predictors, y = response, training_frame = train,
		                        validation_frame = valid, col_sample_rate_per_tree = 0.7, 
		                        seed = 1234)

		# print the AUC for the validation data
		print(h2o.auc(airlines_gbm, valid = TRUE))


		# Example of values to grid over for `col_sample_rate_per_tree`
		hyper_params <- list( col_sample_rate_per_tree = c(0.3, 0.7, 0.8, 1) )

		# 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")
		# this GBM uses early stopping once the validation AUC doesn't improve by at least 0.01% for
		# 5 consecutive scoring events
		grid <- h2o.grid(x = predictors, y = response, training_frame = train, validation_frame = valid,
		                 algorithm = "gbm", grid_id = "air_grid", hyper_params = hyper_params,
		                 stopping_rounds = 5, stopping_tolerance = 1e-4, stopping_metric = "AUC",
		                 search_criteria = list(strategy = "Cartesian"), seed = 1234)

		## Sort the grid models by AUC
		sorted_grid <- h2o.getGrid("air_grid", sort_by = "auc", decreasing = TRUE)
		sorted_grid


   .. code-tab:: python

		import h2o
		from h2o.estimators.gbm import H2OGradientBoostingEstimator
		h2o.init()

		# import the airlines dataset:
		# This dataset is used to classify whether a flight will be delayed 'YES' or not "NO"
		# original data can be found at http://www.transtats.bts.gov/
		airlines= h2o.import_file("https://s3.amazonaws.com/h2o-public-test-data/smalldata/airlines/allyears2k_headers.zip")

		# convert columns to factors
		airlines["Year"]= airlines["Year"].asfactor()
		airlines["Month"]= airlines["Month"].asfactor()
		airlines["DayOfWeek"] = airlines["DayOfWeek"].asfactor()
		airlines["Cancelled"] = airlines["Cancelled"].asfactor()
		airlines['FlightNum'] = airlines['FlightNum'].asfactor()

		# set the predictor names and the response column name
		predictors = ["Origin", "Dest", "Year", "UniqueCarrier", "DayOfWeek", "Month", "Distance", "FlightNum"]
		response = "IsDepDelayed"

		# split into train and validation sets 
		train, valid= airlines.split_frame(ratios = [.8], seed = 1234)

		# try using the `col_sample_rate_per_tree` parameter: 
		# initialize your estimator
		airlines_gbm = H2OGradientBoostingEstimator(col_sample_rate_per_tree = .7, seed =1234) 

		# then train your model
		airlines_gbm.train(x = predictors, y = response, training_frame = train, validation_frame = valid)

		# print the auc for the validation data
		print(airlines_gbm.auc(valid=True))


		# Example of values to grid over for `col_sample_rate_per_tree`
		# import Grid Search
		from h2o.grid.grid_search import H2OGridSearch

		# select the values for col_sample_rate_per_tree to grid over
		hyper_params = {'col_sample_rate_per_tree': [.3, .7, .8, 1]}

		# 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 GBM estimator
		# use early stopping once the validation AUC doesn't improve by at least 0.01% for 
		# 5 consecutive scoring events
		airlines_gbm_2 = H2OGradientBoostingEstimator(seed = 1234,
		                                              stopping_rounds = 5,
		                                              stopping_metric = "AUC", stopping_tolerance = 1e-4)

		# build grid search with previously made GBM and hyper parameters
		grid = H2OGridSearch(model = airlines_gbm_2, hyper_params = hyper_params,
		                     search_criteria = {'strategy': "Cartesian"})

		# train using the grid
		grid.train(x = predictors, y = response, training_frame = train, validation_frame = valid)

		# sort the grid models by decreasing AUC
		sorted_grid = grid.get_grid(sort_by = 'auc', decreasing = True)
		print(sorted_grid)