# Flow charts in R

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Flow charts are an important part of a clinical trial report. Making them can be a pain though. One good way to do it seems to be with the grid and Gmisc packages in R. X and Y coordinates can be designated based on the center of the boxes in normalized device coordinates (proportions of the device space – 0.5 is this middle) which saves a lot of messing around with corners of boxes and arrows.

A very basic flow chart, based very roughly on the CONSORT version, can be generated as follows…

library(grid) library(Gmisc) grid.newpage() # set some parameters to use repeatedly leftx <- .25 midx <- .5 rightx <- .75 width <- .4 gp <- gpar(fill = "lightgrey") # create boxes (total <- boxGrob("Total\n N = NNN", x=midx, y=.9, box_gp = gp, width = width)) (rando <- boxGrob("Randomized\n N = NNN", x=midx, y=.75, box_gp = gp, width = width)) # connect boxes like this connectGrob(total, rando, "v") (inel <- boxGrob("Ineligible\n N = NNN", x=rightx, y=.825, box_gp = gp, width = .25, height = .05)) connectGrob(total, inel, "-") (g1 <- boxGrob("Allocated to Group 1\n N = NNN", x=leftx, y=.5, box_gp = gp, width = width)) (g2 <- boxGrob("Allocated to Group 2\n N = NNN", x=rightx, y=.5, box_gp = gp, width = width)) connectGrob(rando, g1, "N") connectGrob(rando, g2, "N") (g11 <- boxGrob("Followed up\n N = NNN", x=leftx, y=.3, box_gp = gp, width = width)) (g21 <- boxGrob("Followed up\n N = NNN", x=rightx, y=.3, box_gp = gp, width = width)) connectGrob(g1, g11, "N") connectGrob(g2, g21, "N") (g12 <- boxGrob("Completed\n N = NNN", x=leftx, y=.1, box_gp = gp, width = width)) (g22 <- boxGrob("Completed\n N = NNN", x=rightx, y=.1, box_gp = gp, width = width)) connectGrob(g11, g12, "N") connectGrob(g21, g22, "N")

Sections of code to make the boxes are wrapped in brackets to print them immediately. The code creates something like the following figure:

For detailed info, see the Gmisc vignette. This code is also on github.

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