Simple data manipulation on a R data frame

Given a data frame df with a variable named Var, to extract the vector containing all the observations for that variable I should use the dollar sign to connect dataframe to its variable:

df$Var

Now, for that variable I can get its mean:

mean(df$Var)

Standard deviation:

sd(df$Var)

Summary (that works also for a complete data frame):

summary(df$Var)

Which observation has the minimum value for the passed variable:

which.min(df$Var)

Which observation has the maximum value for the passed variable:

which.max(df$Var)

It is easy to generate a scattered plot that correlates two variables in a data frame:

plot(df$Var1, df$Var2)

Here Var1 would get the X axis while Var2 the Y axis.

We can extract a subset from a dataframe evaluating conditions on one or more variables:

sub = subset(df, Var1 > 100 & Var2 < 50)

Notice that the AND logical operator is an ampersand. To see how many observations are in this subset (and in any dataframe) we can use the nrow function:

nrow(sub)

To generate an histogram in R we use the hist() function. The boxplot() function generate boxes, that are quite useful to see the statistical range of a variable.