[S] Efficient method for producing a data frame of summary statistics

Frank E Harrell Jr (fharrell@virginia.edu)
Fri, 24 Apr 1998 14:38:41 -0400


What is the most efficient method for creating a data frame containing
vectors of summary statistics? For example, suppose that data frame d
contains age.group, sex, and y. I want to make a new data frame
containing the combinations of age.group and sex that occurred in the
data, along with a new matrix variable or two new variables containing
the 0.25 and 0.75 quantiles. Then I'll pass the new summary data frame
to trellis for graphing results. tapply will do the calculations I
need but the resulting format is a matrix rather than a data frame
containing combinations of stratification variables.

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Frank E Harrell Jr
Professor of Biostatistics and Statistics
Director, Division of Biostatistics and Epidemiology
Dept of Health Evaluation Sciences
University of Virginia School of Medicine
http://www.med.virginia.edu/medicine/clinical/hes/biostat.htm

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