I have a workflow where I need to generate some data in R, generate plots for the data, save the plots, then render them later. I am using SQLite for this. It works fine, but only for ggplot2 plots. When I try to save and re-render base R plots, it does not work. Any ideas? Using R version 3.3.0. Here is my code:
library("ggplot2") library("RSQLite") # test data dat <- data.frame(x = rnorm(50, 1, 6), y = rnorm(50, 1, 8)) # make ggplot g <- ggplot(dat, aes(x = x, y = y)) + geom_point() # make base plot pdf("test.pdf") # need open graphics device to record plot headlessly dev.control(displaylist="enable") plot(dat) p <- serialize(recordPlot(), NULL) dev.off() # make data frame for db insertion df1 <- data.frame(baseplot = I(list(p)), ggplot = I(list(serialize(g, NULL)))) # setup db con <- dbConnect(SQLite(), ":memory:") dbGetQuery(con, 'create table graphs (baseplot blob, ggplot blob)') # insert the data dbGetPreparedQuery(con, 'insert into graphs (baseplot, ggplot) values (:baseplot, :ggplot)', bind.data=df1) # get the data back out df2 <- dbGetQuery(con, "select * from graphs") # print the ggplot; not sure why I need 'lapply' for this to work... lapply(df2[["ggplot"]][1], "unserialize") # print the base plot lapply(df2[["baseplot"]][1], "unserialize") # Error: NULL value passed as symbol address 1 Answers
Answers 1
Partial answer to record my findings: I cannot say why this is happening, but this is not related to sqlite. The same error occurs right after serializing the plot:
dat <- data.frame(x = rnorm(50, 1, 6), y = rnorm(50, 1, 8)) pdf("test.pdf") # need open graphics device to record plot headlessly dev.control(displaylist="enable") plot(dat) p <- serialize(recordPlot(), NULL) dev.off() unserialize(p) # !! Error: NULL value passed as symbol address 
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