Data Science Tutorial Part 6 Data Frames

1. Data frames

1. In simple words a data frame is a table
2. Rows are called as observations
3. Columns are called as variables
4. Columns can be different data types
5. One column should store only one datatype data
6. Create data frame
1. Generally we are going to create data frame by importing csv files,relational database,excel ..etc
2. First let us see how to create manually
   
   
7. Structure of the data frame .Notice that above data frame has 3 observations(rows) and 4 variables(columns)
   
   
8. In create data frame include one more parameter stringsAsFactors = FALSE and observe str(emp.data)
9. Summary of data in data frame
   
   
10. Exercise : create one more dataframe with the name df and with below data
    
11. Extract specific column of a data frame using column name
    
    
12. Extract the first two rows and then all columns
    
13. Extract the first two columns and then all rows
    
14. Extract specific rows and columns

15. Add a column to data frame
    
    
16. Add row to data frame
    
    
    
    
17. Delete a row from data frame
    
    
18. Delete column from data frame
    
    
19. Head(),tail(),dim() functions

20. Sort() and order() functions
    
21. The number of data rows in the data frame is given by the nrow() function
22. the number of columns of a data frame is given by the ncol() function
1. 
23. We reference a data frame column with the double square bracket "[[]]" operator.
24. For example, to retrieve the ninth column vector of the built-in data set mtcars, we write mtcars[[9]] or mtcars[["am"]] or mtcars$am or mtcars[,"am"]

For more refer https://cran.r-project.org/doc/manuals/R-intro.html#Data-frames or http://www.r-tutor.com/r-introduction/data-frame