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A DataFrame (table like datastructure) for Python, similar to R's dataframe based on numpy arrays

Project description

An implemention of an almost R like DataFrame object.
u = DataFrame( { "Field1": [1, 2, 3],
"Field2": ['abc', 'def', 'hgi']},
['Field1', 'Field2']
["rowOne", "rowTwo", "thirdRow"])

A DataFrame is basically a table with rows and columns.

Columns are named, rows are numbered (but can be named) and can be easily selected and calculated upon. Internally, columns are stored as 1d numpy arrays. If you set row names, they're converted into a dictionary for fast access. There is a rich subselection/slicing API, see help(DataFrame.get_item) (it also works for setting values). Please note that any slice get's you another DataFrame, to access individual entries use get_row(), get_column(), get_value().

DataFrames also understand basic arithmetic and you can either add (multiply,...) a constant value, or another DataFrame of the same size / with the same column names, like this:
#multiply every value in ColumnA that is smaller than 5 by 6.
my_df[my_df[:,'ColumnA'] < 5, 'ColumnA'] *= 6

#you always need to specify both row and column selectors, use : to mean everything
my_df[:, 'ColumnB'] = my_df[:,'ColumnA'] + my_df[:, 'ColumnC']

#let's take every row that starts with Shu in ColumnA and replace it with a new list (comprehension)
select = my_df.where(lambda row: row['ColumnA'].startswith('Shu'))
my_df[select, 'ColumnA'] = [row['ColumnA'].replace('Shu', 'Sha') for row in my_df[select,:].iter_rows()]

Dataframes talk directly to R via rpy2 (rpy2 is not a prerequiste for the library!)
from dataframe import DataFrame
from rpy2 import robjects as ro
my_df = DataFrame({"ColumnA": [1,2,3], 'ColumnB': ['sha','sha','shu']})

Combine DataFrames on rows or columns:
my_df = a.rbind_copy(b) # a and b have the same columns
my_df = a.cbind_view(b) # my_df is a composite sharing numpy arrays (columns) with a and b
my_d = a.join_columns_on(b, 'Name_in_A', 'Name_in_B") #join on common values

#manipulate DataFrame columns
my_df.insert_column("new_column_name", [1,2, 3])
my_df.drop_all_columns_except('keep_me_please', 'keep_me_as_well')
print my_df.get_column_names()
my_df.impose_partial_column_order(['FirstColumn','Second_Column'],['pen_ultimate_column','ultimate_column']) # set the column order. Everything between the first and the second list (unspecified columns) get's sorted alphabetically

#access data
my_df[100, "ColumnA"] #a new DataFrame with one column and one row
my_df.get_value(100, 'ColumnA') #whatever was in in row 100, column 'ColumnA' (string, int, object...)
my_df.get_row(100) # -> {"ColumnA": value, "ColumnB": another_value}
my_df.get_row_as_list(100) # -> [value, another_value], in order of my_df.columns_ordered
my_df.get_column('columnA') # numpy array of the column (a copy)
my_df.get_column_view('columnA') # the actual underlying numpy array

#iterate across the data
my_df.iter_rows() # iter rows as dictionarys
my_df.iter_rows_as_list() # iter rows as lists (see get_row_as_list())
my_df.iter_values_columns_first() #value by value, first column row 1, first column row 2...
my_df.iter_values_rows_first() #value by value, first column, row 1, second column, row 1

#turn into boolean array for subselection
my_df.where(lambda row: row['ColumnA'].startswith("Hello") and row['ColumnB'] >=5)
my_df[:,"Just_one_column"] > 5 # any comparison

sorted_df = my_df.sort_by("ColumnA") # copy sorted by ColumnA ascending
sorted_df = my_df.sort_by("ColumnA", False) # copy sorted by ColumnA descending
sorted_df = my_df.sort_by(["ColumnA", 'ColumnB'], [False, True]) # copy sorted by ColumnA descending, then Column B ascending

#aggregation functions
my_df.mean('ColumnA') # - average (mean) of the values in ColumnA
my_df.mean_and_std('ColumnA') # - mean and standard deviation of the values in ColumnA

#translate columns
my_df.turn_into_level('ColumnA') #turns into R compatible factor. Optional: order of levels
my_df.digitize_column('ColumnA') # bin the values
my_df.rankify_column('ColumnA', True) # turn into ranks, Ascending (0.5, 0.6, 0.55) -> 0, 2, 1
my_df.rescale_column_0_1('ColumnA') # rescales a column to lie within 0..1 (inclusive)

#import and export
my_df = pydataframe.DF2CSV().read("filename", dialect=pydataframe.TabDialect(), handle_quotes=True) #read a tab seperated value file. Lot's of options, please check the code
pydataframe.DF2CSV().write(my_df, filename, dialect=pydataframe.TabDialect()) # write a tab seperated value file

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