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I have recently been using the Lavaan package in R for Structural Equations Modeling and use the semPlot package, which seems to piggyback off of qgraph, in generating path diagrams.

I have found that qgraph has support for plotting images (such as jpeg and png) as nodes.

My question is whether it is possible, and if so how, to graph a different image for each node in a path diagram. I would love to be able to use pictures of my study's items to fill in for the manifest variables on my path diagram. Thanks!

oz123
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StaticStudent
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1 Answers1

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and thank you for checking out semPlot (which is still in a very developmental state). You can certainly do this. Indeed semPlot piggybacks off qgraph, in fact it is basically a frontend to qgraph and returns a qgraph object. You can send arguments to qgraph or plot the result again with different arguments. For example:

library("lavaan")

# Example 5.8 from mplus user guide:
Data <- read.table("http://www.statmodel.com/usersguide/chap5/ex5.8.dat")
names(Data) <- c(paste("y", 1:6, sep=""),
                 paste("x", 1:3, sep=""))

# Model:
model.Lavaan <- 'f1 =~ y1 + y2 + y3
f2 =~ y4 + y5 + y6
f1 + f2 ~ x1 + x2 + x3 '

# Run Lavaan:
library("lavaan")
fit <- lavaan:::cfa(model.Lavaan, data=Data, std.lv=TRUE)

# Download R logo:
download.file("http://cran.r-project.org/Rlogo.jpg", file <- tempfile(fileext = ".jpg"), 
              mode = "wb")

# Plot path diagram and store qgraph object:
Graph <- semPaths(fit,title=FALSE, curvePivot = TRUE)

# plot qgraph again with images:
qgraph(Graph, images = file, labels = FALSE)

If you want to use a different image per node, you can give images a vector contaning the file names of the images for each node in the order of the nodes. To find out the node order you can do:

# To see which nodes are which:
Graph$graphAttributes$Nodes$labels
Sacha Epskamp
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  • Thanks so much for this! I have one more question, being very new to this. Assuming I wanted to import my own jpeg files (not download one), would it be easiest to use readJPEG of the jpeg package and then rasterImage from the graphics package or is there a better way? – StaticStudent Mar 28 '13 at 13:56
  • You should just give the filename/path to images. The download here is just to have an example, note that `file`, which is used in the `qgraph` call, is just a string linking to a temporary file. – Sacha Epskamp Mar 29 '13 at 03:58