Adding a column of means by group to original data
7274
Calculate group mean (or other summary stats) and assign to original data
87266
Apply several summary functions on several variables by group in one call
38204
Fitting linear model / ANOVA by group
149949
How to create multiple rows combining data sets
24411
Aggregate / summarize multiple variables per group (e.g. sum, mean)
81713
How to add an extra column to a current matrix (list)?
109959
Calculate mean of ordinal variable
53276
Group data and plot multiple lines
63930
How can I "group by" and sum a column in excel?
156981
Generating data with a given sample covariance matrix
156460
Expanding a dataset based on a weight field
89750
Writing python script to group and sum records from each group?
5136
How to sum a variable by group
8801
Can I combine the results from multiple columns into a single column without UNION?
147397
How do I combine two data-frames based on two columns?
48696
Combine (rbind) data frames and create column with name of original data frames
94756
Join two files, adding values in certain columns