describe.by {psych} | R Documentation |
Report basic summary statistics by a grouping variable. Useful if the grouping variable is some experimental variable and data are to be aggregated for plotting. Partly a wrapper for by and describe
describe.by(x, group,mat=FALSE,...)
x |
a data.frame or matrix |
group |
a grouping variable or a list of grouping variables |
mat |
provide a matrix output rather than a list |
... |
parameters to be passed to describe |
To get descriptive statistics for several different grouping variables, make sure that group is a list. In the case of matrix output with multiple grouping variables, the grouping variable values are added to the output.
A data.frame of the relevant statistics broken down by group:
item name
item number
number of valid cases
mean
standard deviation
median
mad: median absolute deviation (from the median)
minimum
maximum
skew
standard error
William Revelle
data(sat.act) describe.by(sat.act,sat.act$gender) #just one grouping variable #describe.by(sat.act,list(sat.act$gender,sat.act$education)) #two grouping variables des.mat <- describe.by(sat.act$age,sat.act$education,mat=TRUE) #matrix (data.frame) output des.mat <- describe.by(sat.act$age,list(sat.act$education,sat.act$gender),mat=TRUE) #matrix output