r - Saving plots within lapply

Question

I have a list of dataframes:

str(subsets.d)
List of 22
 $ 1       :'data.frame':   358 obs. of  118 variables:
  ..$ Ac_2017_1 : num [1:358] 0 0 0 0 0 0 0 0 0 0 ...
  ..$ Ac_9808_1 : num [1:358] 0 0 0 0 0 ...
  ..$ dates     : Ord.factor w/ 6 levels "April"<"May"<..: 1 1 1 1 1 1 1 
 $ 19      :'data.frame':   358 obs. of  2 variables:
  ..$ Ac_8598_19: num [1:358] 0.000257 0.000288 0.000171 0 0.000562 ...
  ..$ dates     : Ord.factor w/ 6 levels "April"<"May"<..: 1 1 1 1 1 1 1 

I proceed by transforming this into long formats:

library(reshape2)
subsets.m <- lapply(subsets.d, function(x) melt(x))

and then i want to produce boxplots by dates:

library(ggplot2)
lapply(subsets.m, function(x)
  ggplot(x, aes(dates, value)) + geom_boxplot() + facet_wrap(~variable, scale="free_y"))

Is it possible to put a ggsave() or pdf() inside or otside the lapply? if so, how can i name the saved plots according to the dataframe?

Bonus question, since the dataframes inside the list have different dimensions, the plots can differ in size. Can i adjust for that?

Here is some small example data:

dput(list1)
list(structure(list(Ac_7595_JG37 = c(0.000128383, 0.000576914, 
0.000341631, 0.000729133, 0.000187486, 0.00086127, 0.000594978, 
0.000631912, 0.000502274, 0.0004846, 0, 0.000148386, 0.000298153, 
0.000828969, 0.000436815, 7.28336e-05, 0.000304842, 0.000301909, 
0.000233694, 0.000208491), Ac_7474_JG37 = c(0, 0, 0.000512446, 
0, 0.000562457, 0, 0.000198326, 0.000473934, 0, 0.000138457, 
0.000132554, 0, 0.000198769, 0.000207242, 0.000145605, 0.000364168, 
0, 0.000301909, 0.000116847, 0), dates = structure(c(1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
2L, 2L), .Label = c("April", "May", "June", "August", "October", 
"November"), class = c("ordered", "factor"))), .Names = c("Ac_7595_JG37", 
"Ac_7474_JG37", "dates"), row.names = c("1", "2", "3", "4", "5", 
"6", "7", "8", "9", "10", "61", "62", "63", "64", "65", "66", 
"67", "68", "69", "70"), class = "data.frame"), structure(list(
    Ac_8732_20 = c(0.000513534, 0.000384609, 0.000341631, 0.000729133, 
    0.000937429, 0.000322976, 0.000297489, 0.000394945, 0.000669698, 
    0.000346143, 0.000265108, 0.000296773, 0.000596306, 0.000310863, 
    0, 0.000509835, 0, 0.000301909, 0.000233694, 0), dates = structure(c(1L, 
    1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 
    2L, 2L, 2L, 2L), .Label = c("April", "May", "June", "August", 
    "October", "November"), class = c("ordered", "factor"))), .Names = c("Ac_8732_20", 
"dates"), row.names = c("1", "2", "3", "4", "5", "6", "7", "8", 
"9", "10", "61", "62", "63", "64", "65", "66", "67", "68", "69", 
"70"), class = "data.frame"))

Answer 1

Your plots are stored in a list, hence you can use lapply on the output to save all of them. This has been answered here: Saving a list of plots by their names()

# create data for this example (data above too involved)
df <- data.frame(value = rnorm(100), dates = rep(1:50, 2), type = rep(c("a", "b")))
list1 <- split(df, df$type)


plots <- lapply(list1, function(x) ggplot(x, aes(dates, value)) + geom_boxplot())

lapply(names(plots), 
       function(x) ggsave(filename=paste(x,".jpeg",sep=""), plot=plots[[x]]))