dplyr_join_challenges.R

set.seed(100)
df1 <- data.frame(a=rep(1:3, each=4), b=round(runif(12, 10, 20)))
df2 <- data.frame(a=0:1, c=10:11)


# You have two dataframe df1 and df2 from the code below. df1 and df2 have column a in common. 
# The challenge for this video is as follows:

# 1. From df1, remove the rows that are present in df2, based on the common column a.
# 2. Create another dataframe df3 that contains all the rows and columns from both datasets.
# 3. In df2, rename column a as `apple` in df2 and create a new dataframe named 'df4' that 
#    contains only the common rows in df1 and df2.
# 4. In df1, for each unique value of column a, compute the mean, first, second, last 
#    and second last value of column 'b' in separate columns.