Handling exception “Argument python_obj should be a …”

Recently I hit the following exception when running python code with H2O functions on a new machine however this exception does not happen on my main machine. The exception was as below:

H2OTypeError: Argument `python_obj` should be a None | list | tuple | dict | numpy.ndarray | pandas.DataFrame | scipy.sparse.issparse, got H2OTwoDimTable
Error in sys.excepthook:
Traceback (most recent call last):
 File “/usr/local/lib/python2.7/site-packages/h2o/utils/debugging.py”, line 95, in _except_hook
 _handle_soft_error(exc_type, exc_value, exc_tb)
 File “/usr/local/lib/python2.7/site-packages/h2o/utils/debugging.py”, line 225, in _handle_soft_error
 args_str = _get_args_str(func, highlight=highlight)
 File “/usr/local/lib/python2.7/site-packages/h2o/utils/debugging.py”, line 316, in _get_args_str
 s = str(inspect.signature(func))[1:-1]

The following message is worth to explore:

Argument python_obj should be a None | list | tuple | dict | numpy.ndarray | pandas.DataFrame | scipy.sparse.issparse, got H2OTwoDimTable


  • The method is looking for numpy, pandas, scipy to be available in the machine
  • I checked that numpy was installed but pandas was missing
  • The missing pandas library gave me cryptic error message


After installing pandas library the problem was resolved.

Thats it, enjoy!!


Exploring & transforming H2O Data Frame in R and Python

Sometime you may need to ingest a dataset for building models and then your first task is to explore all the features and their type you have. Once that is done you may want to change the feature types to the one you want.

Here is the code snippet in Python:

df = h2o.import_file('https://raw.githubusercontent.com/h2oai/sparkling-water/master/examples/smalldata/prostate.csv')
{    u'AGE': u'int', u'CAPSULE': u'int', u'DCAPS': u'int', 
     u'DPROS': u'int', u'GLEASON': u'int', u'ID': u'int',
     u'PSA': u'real', u'RACE': u'int', u'VOL': u'real'
If you would like to visualize all the features in graphical format you can do the following:
import pylab as pl
The result looks like as below on jupyter notebook:
Screen Shot 2017-10-05 at 5.20.03 PM
Note: If you have features above 50, you might have to trim your data frame to less features so you can have effective visualization.
Next you may need to You can also use the following function to convert a list of columns as factor/categorical by passing H2O dataframe and a list of columns:
def convert_columns_as_factor(hdf, column_list):
    list_count = len(column_list)
    if list_count is 0:
        return "Error: You don't have a list of binary columns."
    if (len(pdf.columns)) is 0:
        return "Error: You don't have any columns in your data frame."
    local_column_list = pdf.columns
    for i in range(list_count):
            target_index = local_column_list.index(column_list[i])
            pdf[column_list[i]] = pdf[column_list[i]].asfactor()
            print('Column ' + column_list[i] + " is converted into factor/catagorical.")
        except ValueError:
            print('Error: ' + str(column_list[i]) + " not found in the data frame.")

The following script is in R to perform the same above tasks:

color = sample(c("D","E","I","F","M"),size=N,replace=TRUE)
num = rnorm(N,mean = 12,sd = 21212)
sex = sample(c("male","female"),size=N,replace=TRUE)
sex = as.factor(sex)
color = as.factor(color)
data = sample(c(0,1),size = N,replace = T)
fdata = factor(data)
dd = data.frame(color,sex,num,fdata)
data = as.h2o(dd)
data$sex = h2o.setLevels(x = data$sex ,levels = c("F","M"))
Thats it, enjoy!!

H2O Word2Vec Tutorial with example in Scala

If you would like to know what is word2vec and why you should use it, there is lots of material available to scan.  You can learn more about H2O implementation of Word2Vec here, along with its configuration and interpretation.

In this Scala example we will use H2O Word2Vec algorithm to build a model using the given Text (as text file, or an Array) and then build Word2vec model from it.

Here is the full Scala code of the following example at my github.

Lets start H2O cluster first:

import org.apache.spark.h2o._
val h2oContext = H2OContext.getOrCreate(spark)

Now we will be importing required libraries to get our job done:

import scala.io.Source
import _root_.hex.word2vec.{Word2Vec, Word2VecModel}
import _root_.hex.word2vec.Word2VecModel.Word2VecParameters
import water.fvec.Vec

Now we will be creating a stop words list which are not useful for text mining and removed from the word source:

val STOP_WORDS = Set("ourselves", "hers", "between", "yourself", "but", "again", "there", "about", 
    "once", "during", "out", "very", "having", "with", "they", "own", "an", "be", "some", "for", "do", 
    "its", "yours", "such", "into", "of", "most", "itself", "other", "off", "is", "s", "am", "or", "who", "as", 
     "from", "him", "each", "the", "themselves", "until", "below", "are", "we", "these", "your", "his", "through", "don", "nor", "me", "were", "her", 
    "more", "himself", "this", "down", "should", "our", "their", "while", "above", "both", "up", 
    "to", "ours", "had", "she", "all", "no", "when", "at", "any", "before", "them", "same", "and", "been", "have", "in", "will", "on", "does", "yourselves", "then", "that", "because", "what", "over", "why", "so", "can", 
    "did", "not", "now", "under", "he", "you", "herself", "has", "just", "where", "too", "only", "myself", "which", "those", "i", "after", "few", "whom", "t", "being", "if", "theirs", "my", "against", "a", "by", "doing", 
    "it", "how", "further", "was", "here", "than")


Now lets ingest the text data we would want to run Word2Vec algorithms to vectorize the data first and then run machine learning experiment to it.

I have downloaded a free story “The Adventure of Sherlock Holmes” from Internet and using that as my source.  

val filename = "/Users/avkashchauhan/Downloads/TheAdventuresOfSherlockHolmes.txt"
val lines = Source.fromFile(filename).getLines.toArray
val sparkframe = sc.parallelize(lines)

Now lets defined the tokenize function which will convert out input text to tokens:

def tokenize(line: String) = {
 //get rid of nonWords such as punctuation as opposed to splitting by just " "

//Lets remove stopwords defined above
 .filterNot(word => STOP_WORDS.contains(word)) :+ null

Now we will be calling the tokenize function to create a list of labeled words:

val allLabelledWords = sparkframe.flatMap(d => tokenize(d))

Note: You can also use your own or a custom tokenize function from a library as well, you just need to map the function to the DataFrame.

Now lets convert the collection of label words into an H2O DataFrame:

val h2oFrame = h2oContext.asH2OFrame(allLabelledWords)

Here is the time now to use the H2O Word2Vec algorithm by configuring the parameters first:

val w2vParams = new Word2VecParameters
w2vParams._train = h2oFrame._key
w2vParams._epochs = 500
w2vParams._min_word_freq = 0
w2vParams._init_learning_rate = 0.05f
w2vParams._window_size = 20
w2vParams._vec_size = 20
w2vParams._sent_sample_rate = 0.0001f

Now we will perform the real action, building the model:

val w2v = new Word2Vec(w2vParams).trainModel().get()

Now we can apply the model to perform some actions on it:

Lets start first test by finding synonyms using this given word2vec model. We will be calling findSynonyms method by passing a given word  to find N synonyms, the results will be the top ‘count’ synonyms with their distance values:

w2v.findSynonyms("love", 3)
w2v.findSynonyms("help", 2)
w2v.findSynonyms("hate", 1)

Lets Transform words using w2v model and aggregate method average:

The transform() function takes an H2O Vec as the first parameter, where the vector needs to be extracted from the H2O frame h2oFrame.

val newSparkFrame = w2v.transform(h2oFrame.vec(0), Word2VecModel.AggregateMethod.NONE).toTwoDimTable()

Thats it, enjoy!!


Full working example of connecting Netezza from Java and python

Before start connecting you must make sure you can access the Netezza database and table from the machine where you are trying to run Java and or Python samples.

Connecting Netezza server from Python Sample

Check out my Ipython Jupyter Notebook with Python Sample

Step 1: Importing python jaydebeapi library

import jaydebeapi

Step 2: Setting Database connection settings

dsn_database = "avkash"            
dsn_hostname = "" 
dsn_port = "5480"                
dsn_uid = "admin"        
dsn_pwd = "password"      
jdbc_driver_name = "org.netezza.Driver"
jdbc_driver_loc = "/Users/avkashchauhan/learn/customers/netezza/nzjdbc3.jar"
###jdbc:netezza://" + server + "/" + dbName ;
url = '{0}:user={1};password={2}'.format(connection_string, dsn_uid, dsn_pwd)
print("URL: " + url)
print("Connection String: " + connection_string)

Step 3:Creating Database Connection

conn = jaydebeapi.connect("org.netezza.Driver", connection_string, {'user': dsn_uid, 'password': dsn_pwd},
                         jars = "/Users/avkashchauhan/learn/customers/netezza/nzjdbc3.jar")
curs = conn.cursor()

Step 4:Processing SQL Query

curs.execute("select * from allusers")
result = curs.fetchall()
print("Total records: " + str(len(result)))

Step 5: Printing all records

for i in range(len(result)):

Step 6: Closing all connections


Connecting Netezza server from Java Code Sample

Step 1: Have the Netezza driver as nzjdbc3.jar in a folder.

Step 2: Create netezzaJdbcMain.java as below in the same folder where nzjdbc3.jar is placed.

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class netezzaJdbcMain {
    public static void main(String[] args) {
        String server = "x.x.x.x";
        String port = "5480";
        String dbName = "_db_name_";
        String url = "jdbc:netezza://" + server + "/" + dbName ;
        String user = "admin";
        String pwd = "password";
        String schema = "db_schema";
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;
        try {
            System.out.println(" Connecting ... ");
            conn = DriverManager.getConnection(url, user, pwd);
            System.out.println(" Connected "+conn);
            String sql = "select * from allusers";
            st = conn.createStatement();
            rs = st.executeQuery(sql);

            System.out.println("Printing result...");
            int i = 0;
            while (rs.next()) {
                String userName = rs.getString("name");
                int year = rs.getInt("age");
                System.out.println("User: " + userName +
                        ", age is: " + year);
            if (i==0){
                System.out.println(" No data found");
        } catch (Exception e) {
        } finally {
            try {
                if( rs != null) 
                if( st!= null)
                if( conn != null)
            } catch (SQLException e1) {

Step 3: Compile code as below:

$ javac -cp nzjdbc3.jar -J-Xmx2g -J-XX:MaxPermSize=128m netezzaJdbcMin.java                                                                                                                                
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=128m; support was removed in 8.0

Note: You should see your main class is compiled without any problem.

Step 4: Run compiled class as below:

$ java -cp .:nzjdbc3.jar netezzaJdbcMain

 Connecting ...
 Connected org.netezza.sql.NzConnection@3feba861
Printing result...
User: John                , age is: 30
User: Jason               , age is: 26
User: Jim                 , age is: 20
User: Kyle                , age is: 21
User: Kim                 , age is: 27

Note: You will see results something as above.

Thats it, enjoy!!

Python example of building GLM, GBM and Random Forest Binomial Model with H2O

Here is an example of using H2O machine learning library and then building GLM, GBM and Distributed Random Forest models for categorical response variable.

Lets import h2o library and initialize the H2O machine learning cluster:

import h2o

Importing dataset and getting familiar with it:

df = h2o.import_file("https://raw.githubusercontent.com/h2oai/sparkling-water/master/examples/smalldata/prostate.csv")

Lets configure our predictors and response variables from the ingested dataset:

x = df.col_names
print("Response = " + y)
print("Pridictors = " + str(x))

Now we need to set the response column as categorical or factor:

df['CAPSULE'] = df['CAPSULE'].asfactor()

Now we will the levels in our response variable:


[['0', '1']]

Note: Because there are only 2 levels or values, the model will be called Binomial model.

Now we will split our dataset into training, validation and testing datasets:

train, valid, test = df.split_frame(ratios=[.8, .1])

Lets build Generalized Linear Regression (Logistic – response variable is categorical) model first:

from h2o.estimators.glm import H2OGeneralizedLinearEstimator
glm_logistic = H2OGeneralizedLinearEstimator(family = "binomial")
glm_logistic.train(x=x, y= y, training_frame=train, validation_frame=valid, 

Now we will take a look at few model metrics:

Warning: This model doesn't have variable importances

Lets have a look at model coefficients:


Lets perform the prediction using the testing dataset:


Now we are checking the model performance metrics “rmse” based on testing and other datasets:


Now we are checking the model performance metrics “r2” based on testing and other datasets:


Lets build Gradient Boosting Model now:

from h2o.estimators.gbm import H2OGradientBoostingEstimator
gbm = H2OGradientBoostingEstimator()
gbm.train(x=x, y =y, training_frame=train, validation_frame=valid)

Now get to know our model metrics, starting with confusion metrics first:


Now have a look at variable importance plots:


Now have a look at the variable importance table:


Lets build Distributed Random Forest model:

from h2o.estimators.random_forest import H2ORandomForestEstimator
drf = H2ORandomForestEstimator()
drf.train(x=x, y = y, training_frame=train, validation_frame=valid)

lets understand random forest model metrics starting confusion metrics:


We can have a look at gains and lift table also:



  • We can get all model metrics as other model type as applied.
  • We can also get model perform based on training, validation and testing data for all models.

Thats it, enjoy!!


Visualizing H2O GBM and Random Forest MOJO Models Trees in python

In this example we will build a tree based model first using H2O machine learning library and the save that model as MOJO. Using GraphViz/Dot library we will extract individual trees/cross validated model trees from the MOJO and visualize them. If you are new to H2O MOJO model, learn here.

You can also get full working Ipython Notebook for this example from here.

Lets build the model first using H2O GBM algorithm. You can also use Distributed Random Forest Model as well for tree visualization.

Let’s first import key python models:

import h2o
import subprocess
from IPython.display import Image

Now we will be building GBM Model using a public PROSTATE dataset:

df = h2o.import_file('https://raw.githubusercontent.com/h2oai/sparkling-water/master/examples/smalldata/prostate.csv')
x = df.col_names
df[y] = df[y].asfactor()
train, valid, test = df.split_frame(ratios=[.8,.1])
from h2o.estimators.gbm import H2OGradientBoostingEstimator
gbm_cv3 = H2OGradientBoostingEstimator(nfolds=3)
gbm_cv3.train(x=x, y=y, training_frame=train)

## Getting all cross validated models 
all_models = gbm_cv3.cross_validation_models()
print("Total cross validation models: " + str(len(all_models)))

Now lets set all the default parameters to create the graph tree first and then tree images (in PNG format) in the local disk. Make sure you have a writable path where you can create and save these intermediate files. You also need to provide the path for latest H2O (h2o.jar) which is used to generate MOJO Model.

mojo_file_name = "/Users/avkashchauhan/Downloads/my_gbm_mojo.zip"
h2o_jar_path= '/Users/avkashchauhan/tools/h2o-3/h2o-'
mojo_full_path = mojo_file_name
gv_file_path = "/Users/avkashchauhan/Downloads/my_gbm_graph.gv"

Now lets definie Image file name which we will generate from the Tree ID.  Based on Tree ID the image file will have my_gbm_tree_ID.png file name

image_file_name = "/Users/avkashchauhan/Downloads/my_gbm_tree"
Now we will be downloading GBM MOJO Model by saving to disk:

Now lets define the function to generate graphViz tree from the saved MOJO model:

def generateTree(h2o_jar_path, mojo_full_path, gv_file_path, image_file_path, tree_id = 0):
    image_file_path = image_file_path + "_" + str(tree_id) + ".png"
    result = subprocess.call(["java", "-cp", h2o_jar_path, "hex.genmodel.tools.PrintMojo", "--tree", str(tree_id), "-i", mojo_full_path , "-o", gv_file_path ], shell=False)
    result = subprocess.call(["ls",gv_file_path], shell = False)
    if result is 0:
        print("Success: Graphviz file " + gv_file_path + " is generated.")
        print("Error: Graphviz file " + gv_file_path + " could not be generated.")

Now lets defined the method to generate Tree image as PNG from the saved GraphViz tree:

def generateTreeImage(gv_file_path, image_file_path, tree_id):
    image_file_path = image_file_path + "_" + str(tree_id) + ".png"
    result = subprocess.call(["dot", "-Tpng", gv_file_path, "-o", image_file_path], shell=False)
    result = subprocess.call(["ls",image_file_path], shell = False)
    if result is 0:
        print("Success: Image File " + image_file_path + " is generated.")
        print("Now you can execute the follow line as-it-is to see the tree graph:") 
        print("Image(filename='" + image_file_path + "\')")
        print("Error: Image file " + image_file_path + " could not be generated.")

Note: I had to write 2 steps process above because If I put all in 1 step the process hung after graphviz is created.

Now lets generate tree by passing all parameters defined above and proper TREE ID as the last parameter.

#Just change the tree id in the function below to get which particular tree you want
generateTree(h2o_jar_path, mojo_full_path, gv_file_path, image_file_name, 3)

Now we will be generating PNG Tree Image from the saved GraphViz content.

generateTreeImage(gv_file_path, image_file_name, 3)
# Note: If this step hangs, you can look at "dot" active process in osx and try killing it

Lets visualize the main model tree:

# Just pass the Tree Image file name depending on your tree


Lets Visualize the first Cross Validation tree (Cross Validation ID- 1)

# Just pass the Tree Image file name depending on your tree


Lets Visualize the first Cross Validation tree (Cross Validation ID- 2)

# Just pass the Tree Image file name depending on your tree


Lets Visualize the first Cross Validation tree (Cross Validation ID- 3)

Just pass the Tree Image file name depending on your tree



After looking at these tree, you can visualize how the decision are made.

Helpful documentation:

Thats it, enjoy!!

Reading nested parquet file in Scala and exporting to CSV

Recently we were working on a problem where the parquet compressed file had lots of nested tables and some of the tables had columns with array type and our objective was to read it and save it to CSV.

We wrote a script in Scala which does the following

  • Handles nested parquet compressed content
  • Look for columns as “Array” and then remove those columns

Here is a the script

def flattenSchema(schema: StructType, prefix: String = null) : Array[Column] = {
  schema.fields.flatMap(f => {
    val colPath = if (prefix == null) s"`${f.name}`" else s"${prefix}.`${f.name}`"

    f.dataType match {
      case st: StructType => flattenSchema(st, colPath)
      // Skip user defined types like array or vectors
      case x if x.isInstanceOf[ArrayType] => Array.empty[Column]
      case _ => Array(col(colPath).alias(colPath.replaceAll("[.`]", "_")))

Here are the all the steps you would need to take while reading the parquet compressed content and then exporting it to disk as CSV.

val spark = new org.apache.spark.sql.SQLContext(sc)
import org.apache.spark.sql.types._
import org.apache.spark.sql.Column
import org.apache.spark.sql.types._
import org.apache.spark.sql.functions._

scala> :paste
// Entering paste mode (ctrl-D to finish)

def flattenSchema(schema: StructType, prefix: String = null) : Array[Column] = {
  schema.fields.flatMap(f => {
    val colPath = if (prefix == null) s"`${f.name}`" else s"${prefix}.`${f.name}`"

    f.dataType match {
      case st: StructType => flattenSchema(st, colPath)
      // Skip user defined types like array or vectors
      case x if x.isInstanceOf[ArrayType] => Array.empty[Column]
      case _ => Array(col(colPath).alias(colPath.replaceAll("[.`]", "_")))

// Exiting paste mode, now interpreting.

flattenSchema: (schema: org.apache.spark.sql.types.StructType, prefix: String)Array[org.apache.spark.sql.Column]

scala >

val df = spark.read.parquet("/user/avkash/test.parquet")


If you want to see the full working scripts with output you can visit any of the following link based on your Spark Version:

  • Here is the full working demo in Spark 2.1.0
  • Here is the full working demo in Spark 1.6.x.

We got some help from the StackOverflow discussion here. Michal K and Michal M helped me to write above solution.

Thats it, enjoy!!