Merging Two Datasets
--------------------

You can use the `merge` function to combine two datasets that share a common column name. By default, all columns in common are used as the merge key; uncommon will be ignored. Also, if you want to use only a subset of the columns in common, rename the other columns so the columns are unique in the merged result.

Note that in order for a merge to work in multinode clusters, one of the datasets must be small enough to exist in every node.  


.. tabs::
   .. code-tab:: r R
   
		# Currently, this function only supports `all.x = TRUE`. All other permutations will fail.
		library(h2o)
		h2o.init()
		
		# Create two simple, two-column R data frames by inputting values, ensuring that both have a common column (in this case, "fruit").
		left <- data.frame(fruit = c('apple', 'orange', 'banana', 'lemon', 'strawberry', 'blueberry'), 
		                   color = c('red', 'orange', 'yellow', 'yellow', 'red', 'blue'))
		right <- data.frame(fruit = c('apple', 'orange', 'banana', 'lemon', 'strawberry', 'watermelon'), 
		                    citrus = c(FALSE, TRUE, FALSE, TRUE, FALSE, FALSE))
		
		# Create the H2O data frames from the inputted data.
		left_frame <- as.h2o(left)
		print(left_frame)
		        fruit  color
		 1      apple    red
		 2     orange orange
		 3     banana yellow
		 4      lemon yellow
		 5 strawberry    red
		 6  blueberry   blue
		
		[6 rows x 2 columns]
		
		right_frame <- as.h2o(right)
		print(right_frame)
		        fruit citrus
		 1      apple  FALSE
		 2     orange   TRUE
		 3     banana  FALSE
		 4      lemon   TRUE
		 5 strawberry  FALSE
		 6 watermelon  FALSE

		[6 rows x 2 columns]
		
		# Merge the data frames. The result is a single dataset with three columns.
		new_frame <- h2o.merge(left_frame, right_frame, all.x = TRUE)
		print(new_frame)
		       fruit  color citrus
		1  blueberry   blue   <NA>
		2      apple    red  FALSE
		3     banana yellow  FALSE
		4      lemon yellow   TRUE
		5     orange orange   TRUE
		6 strawberry    red  FALSE
		
		[6 rows x 3 columns] 
   
   .. code-tab:: python
   
		import h2o
		h2o.init()
		import numpy as np
		
		# Create a dataset by inputting raw data. 
		df1 = h2o.H2OFrame.from_python({'A':['Hello', 'World', 'Welcome', 'To', 'H2O', 'World'], 
		                                'n': [0,1,2,3,4,5]})
		df1.describe
		A          n
		-------  ---
		Hello      0
		World      1
		Welcome    2
		To         3
		H2O        4
		World      5
		
		[6 rows x 2 columns]
		
		# Generate a random dataset from python. 
		df2 = h2o.H2OFrame.from_python([[x] for x in np.random.randint(0, 10, size=20).tolist()], column_names=['n'])
		df2.describe
		  n
		---
		nan
		  0
		  8
		  6
		  1
		  7
		  8
		  5
		  1
		  3
		  
		[21 rows x 1 column]
		
		# Merge the first dataset into the second dataset. Note that only columns 
		# in common are merged (i.e, values in df2 greater than 5 will not be merged).
		df3 = df2.merge(df1)
		df3.describe
		  n  A
		---  -------
		nan  Hello
		  3  To
		  3  To
		  0  Hello
		  5  World
		  3  To
		  0  Hello
		  5  World
		  1  World
		  2  Welcome
		  
		[14 rows x 2 columns]
		
		# Merge all of df2 into df1. Note that this will result in missing values for 
		# column A, which does not include values greater than 5.
		df4 = df2.merge(df1, all_x=True)
		df4.describe
		  n  A
		---  -----
		nan  Hello
		  0  Hello
		  8
		  6
		  1  World
		  7
		  8
		  5  World
		  1  World
		  3  To
		
		[21 rows x 2 columns]