Input, Subset and Output External Data Files using Pandas All Versions

Examples

• 0

  Basic Code to Import, Subset and Write External Data Files Using Pandas
  0

  # Print the working directory
  import os
  print os.getcwd()
  # C:\Python27\Scripts
  
  # Set the working directory
  os.chdir('C:/Users/general1/Documents/simple Python files')
  print os.getcwd()
  # C:\Users\general1\Documents\simple Python files
  
  # load pandas
  import pandas as pd
  
  # read a csv data file named 'small_dataset.csv' containing 4 lines and 3 variables
  my_data = pd.read_csv("small_dataset.csv")
  my_data
  #     x   y   z
  # 0   1   2   3
  # 1   4   5   6
  # 2   7   8   9
  # 3  10  11  12
  
  my_data.shape       # number of rows and columns in data set
  # (4, 3)
  
  my_data.shape[0]    # number of rows in data set
  # 4
  
  my_data.shape[1]    # number of columns in data set
  # 3
  
  # Python uses 0-based indexing.  The first row or column in a data set is located
  # at position 0.  In R the first row or column in a data set is located
  # at position 1.
  
  # Select the first two rows
  my_data[0:2]
  #    x   y   z
  #0   1   2   3
  #1   4   5   6
  
  # Select the second and third rows
  my_data[1:3]
  #    x  y  z
  # 1  4  5  6
  # 2  7  8  9
  
  # Select the third row
  my_data[2:3]
  #    x   y   z
  #2   7   8   9
  
  # Select the first two elements of the first column
  my_data.iloc[0:2, 0:1]
  #    x
  # 0  1
  # 1  4
  
  # Select the first element of the variables y and z
  my_data.loc[0, ['y', 'z']]
  # y    2
  # z    3
  
  # Select the first three elements of the variables y and z
  my_data.loc[0:2, ['y', 'z']]
  #    y  z
  # 0  2  3
  # 1  5  6
  # 2  8  9
  
  # Write the first three elements of the variables y and z
  # to an external file.  Here index = 0 means do not write row names.
  
  my_data2 = my_data.loc[0:2, ['y', 'z']]
  
  my_data2.to_csv('my.output.csv', index = 0)
  

  created Jan 19 at 15:28

  
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