plotting a list of grobs

DISCLOSURE: I'm not sure how to make a reproducible example for this question.

I'm trying to plot a list of grobs using the gridExtra package.

I have some code that looks like this:

## Make Graphic Objects for Spec and raw traces
for (i in 1:length(morletPlots)){
  gridplots_Spec[[i]]=ggplotGrob(morletPlots[[i]])
  gridplots_Raw[[i]]=ggplotGrob(rawPlot[[i]])
  gridplots_Raw[[i]]$widths=gridplots_Spec[[i]]$widths
}
names(gridplots_Spec)=names(morletPlots)
names(gridplots_Raw)=names(rawPlot)

## Combine spec and Raw traces
g=list()
for (i in 1:length(rawPlot)){
    g[[i]]=arrangeGrob(gridplots_Spec[i],gridplots_Raw[i],heights=c(4/5,1/5))
}

numPlots = as.numeric(length(g))

##Plot both
for (i in 1:numPlots){

  grid.draw(g[i],ncol=2)
}

Let me walk through the code.

morletPlots = a list of ggplots

rawplot = A list of ggplots

gridplots_spec and gridplots_Raw = list of grobs from the ggplots made above.

g = a list of the two grobs above combined so combining gridplots_spec[1] and gridplots_raw[1] so on and so on for the length of the list.

now my goal would be two plot all of those into 2 columns. But whenever I pass the gridplots_spec[i] through the grid.draw loop I get an error:

Error in UseMethod("grid.draw") : no applicable method for 'grid.draw' applied to an object of class "list"

I can't unlist it becasue it just turns into a long character vector. any ideas?

If it's absolutely crucial I can spend the time to make an reproducible example but I'm more likely just missing a simple step.

Here's my interpretation of your script, if it's not the intended result you may want to use some bits and pieces to make your question reproducible.

library(grid)
library(gridExtra)
library(ggplot2)

morletPlots <- replicate(5, ggplot(), simplify = FALSE)
rawplot <- replicate(5, ggplot(), simplify = FALSE)

glets <- lapply(morletPlots, ggplotGrob)
graws <- lapply(rawplot, ggplotGrob)

rawlet <- function(raw, let, heights=c(4,1)){
  g <- rbind(let, raw)
  panels <- g$layout[grepl("panel", g$layout$name), ]
#  g$heights <- grid:::unit.list(g$heights) # not needed
  g$heights[unique(panels$t)] <- lapply(heights, unit, "null")
  g
}

combined <- mapply(rawlet, raw = graws, let=glets, SIMPLIFY = FALSE)

grid.newpage()
grid.arrange(grobs=combined, ncol=2)

Edit I can't resist this mischievous hack to colour the plots for illustration; feel free to ignore it.

palette(RColorBrewer::brewer.pal(8, "Pastel1"))
ggplot.numeric = function(i) ggplot2::ggplot() + 
  theme(panel.background=element_rect(fill=i))

morletPlots <- lapply(1:5, ggplot)
rawplot <- lapply(1:5, ggplot)