----------------------------------------------------------------------------- help for parcoord (STB-29: gr18) -----------------------------------------------------------------------------graph multivariate data in parallel coordinates -----------------------------------------------

parcoord varlist [if exp] [in range] [, by(byvar) center colorby(idvar) echo tour graph_options]

Description -----------

parcoord draws a parallel coordinates plot for the variables in varlist. A parallel coordinates plot provides an alternative to the scatterplot matrix for visually examining many variables simultaneously. Variables in varlist are rep- resented as parallel vertical axes; each observation is plotted as a collection of line segments joined end-to-end. Subsets of observations can be selected with if and in clauses; an observation will be ignored if it has missing values for any of the byvar, idvar, or varlist variables.

Options -------

by(byvar) uses the by option of the graph command to draw a separate plot for each value of byvar. The graph option total may be used with this option.

center scales each axis so that the median of the corresponding variable falls at the midpoint and all data fall within the length of the axis. The de- fault is to scale each axis to extend from the minimum to the maximum value of the variable represented.

colorby(idvar) assigns different pens to observations with different values of idvar. On color monitors, this displays subsets of observations (defined by idvar) in different colors.

echo prints the names of the axes (variables), in left-right order, to the Results screen before drawing the plot. (Useful if the number of variables is large and the variable names are hard to read in the plot.)

tour generates a sequence of plots by repeatedly permuting the left-right order of the variables in the plot. By default, axes are drawn in the same order that the variables appear in the varlist. tour permutes the axes such that each possible pair of the p variables in varlist is represented on adjacent axes within the first (p+1)/2 plots of the tour. The tour pauses after each plot and displays --more--. The tour continues endlessly, until the user presses the Break key, although the tour is largely redundant after the first (p+1)/2 plots.

graph_options are any of the options allowed with graph, twoway, except for: by, b2title, connect, noaxis, pen, symbol, tlabel, xlabel, xline, ylabel, yline.

Examples --------

. parcoord ftime*, center (plot all variables whose names begin with ftime. Variables assigned to axes in the same order that they appear in the data set; axes scaled so that the median of each ftime variable is at the axis midpoint.)

. parcoord xa1 xa2 yb1 yb2 yb3 yb4 if time > 50, col(trt) (one 6-dimensional parallel coordinates plot for all cases where time > 50; observations at different values of trt drawn in different colors.)

. parcoord bwt1-bwt12 if !censor, by(site) tour echo (sequence of graphs for cases where censor == 0; each graph contains a par- allel coordinates plot for each value of site. Successive graphs alter the left-right order of the variables bwt1-bwt12 within each plot; that ordering is printed to the Results screen before each graph is drawn.)

Author ------ John R. Gleason Syracuse University 73241.717atcompuserve.com

Also see --------

STB: STB-29 gr18 Manual: [3] by, [3] matrix, [3] pens On-line: help for graph@, scatterplot