R Example Problems

• Write a function called insert(vec, value, pos) where vec is a vector, value is a single scalar (number, boolean or string) and pos is the position in the vector at which the value should be inserted. The function should report an error is an invalid position is specified
• Read in the file data2.csv and then perform count the number of rows that have yes in the columned called y. Do the same thing for no and maybe
• Look up the table function and redo the above question - it should become a one line solution
• Using the above dataset, generate a data.frame where any row that has a value greater than 50 in the z column, will have the value -1 in the x colum
• Since the y column in the above dataset has 3 levels, yes, no and maybe, determine the mean value of the z column for each group. That is, the mean value of z for all rows that have a yes in their y column and so on
• You can do the above question by manually subsetting the data.frame three times. Look up the by function and see if you can rewrite the problem using it - it will be much shorter!
• Make a cumulative plot of x. To do this, you need to calculate the following elements: x[1], x[1]+x[2], x[1]+x[2]+x[3] and so on. The last element will be the sum of all the rows of x. (The R function cumsum will do this for you, but it's instructive to write it yourself)