how to save ggplots as separate R-objects using For loop

Question

It is intended to produce a number of plots and then merge them freely together using multiplot function. Please could you tell me how to save each plot as a separate R-object instead of having it printed as png file:

Examplary dataframe:

 df1 <- data.frame(A = rnorm(50), B = rnorm(50), C = rnorm(50), group = rep(LETTERS[24:25], 25))

we use a for loop to produce pictures and save them in a file:

And the loop to change:

for(i in names(df1)[1:3]) {
  png(paste(i, "png", sep = "."), width = 800, height = 600)
  df2 <- df1[, c(i, "group")]
  print(ggplot(df2) + geom_boxplot(aes_string(x = "group", y = i, fill = "group")) + theme_bw())
  dev.off()
}

Could you please help with changing the code in order to save each plot as R-object on my screen? Big Thanks in advance!

arvi1000 · Accepted Answer · 2014-09-30 13:48:39Z

4

I'm not sure what you are talking about with "merge them freely together using multiplot function", but you can save ggplot objects using the standard assignment operator. Like any R object, they can be stored in a list.

# empty list for storage
gg_list <- list()

# if you must use a loop, loop through an indexing vector
for(i in 1:3) {
  # if you need the i'th name in df1 use:
  names(df1)[i]
  # assign your ggplot call to the i'th position in the list
  gg_list[[i]]  <- ggplot(...)
}

# Now you can recall the ggplots by reference to the list. 
# E.g., display the 1st one:
print(gg_list[[1]])

answered Sep 30, 2014 at 13:48

arvi1000

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Mario Becerra · Accepted Answer · 2015-11-30 15:46:23Z

4

Instead of using a for loop, if you're gonna store in a list you could just use lapply:

df1 <- data.frame(A = rnorm(50), 
                  B = rnorm(50), 
                  C = rnorm(50), 
                  group = rep(LETTERS[24:25], 25))

gg_list <- lapply(names(df1)[1:3], function(i) {
    df2 <- df1[, c(i, "group")]
    ggplot(df2) + 
    geom_boxplot(aes_string(x = "group", y = i, fill = "group")) +
    theme_bw()
})

gg_list[[1]]

You can even save the list in an RDS object:

saveRDS(gg_list, file = "./gg_list.RDS")

answered Nov 30, 2015 at 15:46

Mario Becerra

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baptiste · Accepted Answer · 2014-09-30 22:19:10Z

3

Here's an alternative strategy that I find more straight-forward (no need to fiddle with names and aes_string): melt the data to long format, and plot subsets

 df1 <- data.frame(A = rnorm(50), B = rnorm(50), C = rnorm(50), 
                   group = rep(LETTERS[24:25], 25))

m = reshape2::melt(df1, id="group")

## base plot, all the data
p = ggplot(m) + geom_boxplot(aes(x = group, y = value)) + theme_bw()

## split-and-apply strategy, using the `%+%` operator to change datasets
pl = plyr::dlply(m, "variable", `%+%`, e1 = p)

do.call(gridExtra::grid.arrange, pl)

answered Sep 30, 2014 at 22:19

baptiste

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