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`

```
describeBy(x, group=NULL,mat=FALSE,type=3,digits=15,...)
describe.by(x, group=NULL,mat=FALSE,type=3,...) # deprecated
```

x

a data.frame or matrix. See note for statsBy.

group

a grouping variable or a list of grouping variables

mat

provide a matrix output rather than a list

type

Which type of skew and kurtosis should be found

digits

When giving matrix output, how many digits should be reported?

...

parameters to be passed to describe

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

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.

The type parameter specifies which version of skew and kurtosis should be found. See `describe`

for more details.

An alternative function (`statsBy`

) returns a list of means, n, and standard deviations for each group. This is particularly useful if finding weighted correlations of group means using `cor.wt`

. More importantly, it does a proper within and between group decomposition of the correlation.

`cohen.d`

will work for two groups. It converts the data into mean differences and pools the within group standard deviations. Returns cohen.d statistic as well as the multivariate generalization (Mahalanobis D).

`describe`

, `statsBy`

, `densityBy`

and `violinBy`

, `cohen.d`

, `cohen.d.by`

, and `cohen.d.ci`

as well as `error.bars`

and `error.bars.by`

for other graphical displays.

# NOT RUN { data(sat.act) describeBy(sat.act,sat.act$gender) #just one grouping variable #describeBy(sat.act,list(sat.act$gender,sat.act$education)) #two grouping variables des.mat <- describeBy(sat.act$age,sat.act$education,mat=TRUE) #matrix (data.frame) output des.mat <- describeBy(sat.act$age,list(sat.act$education,sat.act$gender), mat=TRUE,digits=2) #matrix output # }