Summarizing data by category
The summarize() function reduces the columns of a dataframe to a summary. The arguments to the summarize() function are expressions which create new variables a function of the rows of other columns. Here are a couple examples of possible arguments to the summarize() function:
avg.column.1 = mean(column.1)sum.column.2 = sum(column.2)
The group_by() function causes all of the subsequent operations to be performed by group. The arguments to the group_by() function are the names of columns that the result should be grouped by. When the group_by() function is followed by the summarize() function, the summary is applied to each unique group.
The best way to understand the group_by() function is with a demonstration. In the following continuation of dplyr_intro.R, the fuel economy data is grouped by year and summarized by the mean value of barrels08. Additionally, the filter() function is used to filter the data to include only Toyota Camry models.
Note
The barrels08...
