r - How can I attach a list of custom color palettes to a list of ggplot objects without printing each plot object to the screen? -

i have data frame in r in several of columns factors. i'd create series of bar charts showing relative sizes of each of factor levels. want associate own customized color palettes each of factors, , customize final layout of of bars , legends using gridextra package.

i wrote example script think should achieve that, however, obtained rather surprising result:

library(ggplot2) library(grdevices) library(gridextra)  # define dummy data , put in data frame fruit <- factor(c("apple", "orange", "pear", "pear", "pear",                   "orange", "apple", "apple", "apple", "pear")) cheese <- factor(c("cheddar", "mozarella", "gruyere", "gruyere", "gouda",                    "parmesan", "gruyere", "gouda", "mozarella", "cheddar")) mydata <- data.frame(fruit, cheese) mydata$dummy <- 0  # define custom color schemes foodclrs <- list() # plot fruit factor in shades of red h <- c(0.0,  0.0,  0.0) s <- c(0.95, 0.85, 0.45) v <- c(0.45, 0.85, 0.95) foodclrs[[1]] <- hsv(h, s, v) # plot cheese factor in shades of green h <- c(0.33, 0.33, 0.33, 0.33, 0.33) s <- c(0.95, 0.93, 0.85, 0.69, 0.45) v <- c(0.45, 0.69, 0.85, 0.93, 0.95) foodclrs[[2]] <- hsv(h, s, v)  # create vectors individualized text each plot bsiz=20 fillvars <- c("fruit", "cheese") xlabels <- c("fruits", "cheeses") lgdlabels <- c("types of fruit", "types of cheese")  # generate list of plots plots <- list() (ii in 1:2) {   plots[[ii]] <- ggplot(data=mydata) +      geom_bar(aes_string(x="dummy", fill=fillvars[ii]),              position=position_stack(reverse=true)) +     scale_fill_manual(values=foodclrs[[ii]], drop=false) +     theme_bw(base_size=bsiz) +     labs(x=xlabels[ii], y="") +      theme(axis.ticks.y=element_blank(),           axis.text.y=element_blank()) +     guides(fill=guide_legend(title=lgdlabels[ii])) +     coord_flip() #  print(plots[[ii]]) }  # print plots on own custom-shaped grid print(grid.arrange(plots[[1]], plots[[2]], ncol=1, nrow=2)) 

the output of script looks this:

this not expecting: color palette upper bar chart should have been range of shades of red. seems that, although defined plot object plots[[1]] have red color palette associated it, when went print it, either r or ggplot2 (i'm not sure which) decided use recent color palette instead; i.e., 1 associated plots[[2]].

now here's weird part. if uncomment print statement in for loop, 2 individual plots rendered in correct color scheme (for brevity, not bother include either of them here), and, more interestingly, combined bar chart object inside grid.arrange() function displays correct color scheme:

while happy have stumbled across little workaround, i'm curious: why work in first place?

that say, how calling "print" statement @ correct moment inside of for loop causes color palette become permanently attached each ggplot object, when otherwise not?

what's going on here, "underneath hood", speak? , also, there less kludgy way correct problem? example, there other function call instead of print(), color palette attach correctly each plot object, without creating bunch of individual "dummy" plots don't need?

ggplot2 isn't scoping. possible workaround wrap things in function, surprised need force(),

f <- function(var, fill, xlab, lab){   force(fill)   ggplot(data=mydata) +      geom_bar(aes_string(x="dummy", fill=var),              position=position_stack(reverse=true)) +     scale_fill_manual(values=fill) +     theme_bw(base_size=bsiz) +     labs(x=xlab, y="") +     theme(axis.ticks.y=element_blank(),           axis.text.y=element_blank()) +     guides(fill=guide_legend(title=lab)) +     coord_flip() }  pl <- purrr::pmap(.f = f,                    .l = list(var=fillvars, fill=foodclrs,                             xlab=xlabels,lab=lgdlabels))  grid.arrange(grobs=pl, nrow=2)