diff --git a/hdf5_lib.py b/hdf5_lib.py
index e9bb442..3780814 100644
--- a/hdf5_lib.py
+++ b/hdf5_lib.py
@@ -1,6 +1,6 @@
 import pandas as pd
 import h5py
-#import os
+import os
 import sys
 import numpy as np
 
@@ -103,3 +103,84 @@ def read_hdf5_as_dataframe_v2(filename):
 
     return output_dataframe
 
+def create_hdf5_file(input_data, group_by_funcs, extract_attrs_func = None):
+
+    """   
+        group_by_funcs (list of callables): returns a pd.Series, whose unique values denote groups of input_data elements.
+    """
+
+    if not all([callable(func) for func in group_by_funcs]):
+            raise ValueError("'group_by_funcs' must be a list of callables (or functions) that takes input_data as input an returns valid categorical output.")
+    # Check whether input_data is a valid file system path or a dataframe
+
+    check_possible_path = lambda x : os.path.exists(input_data) if isinstance(input_data,str) else False
+
+    if check_possible_path(input_data):
+        file_list = os.listdir(input_data)
+        df = pd.DataFrame(file_list,columns='filename') 
+    elif isinstance(input_data,pd.DataFrame):
+        df = input_data.copy()
+    else:
+        raise ValueError("input_data must be either a valid file-system path or a dataframe.")
+    
+    for i, func in enumerate(group_by_funcs):
+        df['level_'+str(i)+'_groups'] = func(df)
+
+    # 2. Validate group hierarchy, lower level groups must be embedded in higher level groups
+
+    # 3. Create hdf5 file with groups defined by the 'file_group' column
+    #  
+    # Add datasets to groups and the groups and the group's attributes
+
+    return df
+
+def get_filetype(df):
+    return [os.path.splitext(item)[1][1::] for item in df['filename']]
+
+def group_by_filenumber(df):    
+    return [item[0:item.find('_')] for item in df['filename']]
+
+def group_by_df_column(df, column_name: str):
+    """
+    df (pandas.DataFrame): 
+    column_name (str): column_name of df by which grouping operation will take place.  
+    """
+
+    if not column_name in df.columns:
+        raise ValueError("column_name must be in the columns of df.")
+        
+    return df[column_name]
+
+def main():
+
+    # input data frame
+    input_data = read_hdf5_as_dataframe_v2('input_files\\BeamTimeMetaData.h5')
+
+    # Rename column 'name' with 'filename'. get_filetype finds filetypes based on extension of filenames assumed to be located at the column 'filename'.
+    input_data = input_data.rename(columns = {'name':'filename'})
+    # Add column with filetypes to input_data
+    input_data['filetype'] = get_filetype(input_data)
+    print(input_data['filetype'].unique())
+    # Reduce input_data to files of ibw type
+    input_data = input_data.loc[input_data['filetype']=='ibw',:]
+
+
+
+    #group_by_func = lambda df: [item[0:item.find('_')] for item in df['name']]
+
+    #group_by_func
+
+    group_by_sample = lambda x : group_by_df_column(x,'sample')
+    df = create_hdf5_file(input_data,[group_by_filenumber,group_by_sample])
+
+    df['file_group']
+
+    print(df.head())
+
+
+
+
+if __name__ == '__main__':
+
+    main()
+