How do I export multiple plots as png files from R? - r

Question

I have an R script that creates multiple trend plots from tabular data. I need to export each plot as a png file. I have searched and tried (to no avail) using png(). It seems like this should be a relatively easy fix. My code is below. Could someone please offer some suggestions as to how I might solve this dilemma?
library(dplyr)
library(tidyr)
library(readr)
library(ggplot2)
library(magrittr)
library(stringi)
library(lubridate)
library(stats)
#load in datafiles
c_data <- read_csv ("C:/Projects/A_AX_tech_memo/data_analysis/AAX_data_2017_dtcts.csv")
C_data_out <-
c_data %>%
group_by(METHOD_NAME, STD_CON_LONG_NAME, SAMP_SITE_NAME, FILTERED_FLAG) %>%
ungroup() %>%
select(METHOD_NAME, STD_CON_LONG_NAME, SAMP_SITE_NAME, SAMP_DATE, STD_VALUE_RPTD, STD_ANAL_UNITS_RPTD, FILTERED_FLAG, STD_REPORTING_LIMIT, STD_REQUIRED_DETECTION_LIMIT, LAB_QUALIFIER) %>%
rename(Method = METHOD_NAME, Constit = STD_CON_LONG_NAME, Well = SAMP_SITE_NAME, Date = SAMP_DATE, Value = STD_VALUE_RPTD, Unit = STD_ANAL_UNITS_RPTD, Filtered = FILTERED_FLAG, MDL = STD_REPORTING_LIMIT, RDL = STD_REQUIRED_DETECTION_LIMIT, Flag =LAB_QUALIFIER) %>%
mutate(Date = mdy(Date))
dfs <- split(C_data_out, with(C_data_out, interaction(Well, Constit, Filtered)), drop = TRUE)
plotz <- lapply(dfs, function(x){
ggplot(data = x, aes(Date, Value)) +
geom_point(data = x, aes(color = Flag), size = 3) +
ggtitle(paste(x$Well, x$Constit, x$Filtered, sep =".")) +
ylab("ug/L or Pci/L") +
geom_smooth(method = "lm", se = FALSE, rm.na = TRUE) +
geom_hline(aes(yintercept=x$MDL, linetype="MDL"), color ="dark green", lwd=1, lty=2) +
geom_hline(aes(yintercept=x$RDL, linetype="RDL"), color ="purple", lwd=1, lty=2)
})
Here is an example of what I have tried with png:
names <- lapply(dfs, function(x){
ggtitle(paste(x$Well, x$Constit, x$Filtered, sep ="."))
})
plotz <- lapply(dfs, function(x){
mypath <- file.path("C:","plots", paste(names[i], ".png", sep = ""))
png(file=mypath)
ggplot(data = x, aes(Date, Value)) +
geom_point(data = x, aes(color = Flag), size = 3) +
ggtitle(paste(x$Well, x$Constit, x$Filtered, sep =".")) +
ylab("ug/L or Pci/L") +
geom_smooth(method = "lm", se = FALSE, rm.na = TRUE) +
geom_hline(aes(yintercept=x$MDL, linetype="MDL"), color ="dark green", lwd=1, lty=2) +
geom_hline(aes(yintercept=x$RDL, linetype="RDL"), color ="purple", lwd=1, lty=2)
dev.off()
})
This gives me this error:
Error in paste(names[i], ".png", sep = "") : object 'i' not found
Any and all help would be much appreciated.

Answer 1

This snippet works using the map and walk functions from purrr.
mtcars_split <-
mtcars %>%
split(.$cyl)
paths <-
paste0(names(mtcars_split),".png")
plots <-
mtcars_split %>%
map(~ ggplot(data=.,mapping = aes(y=mpg,x=wt)) + geom_point())
pwalk(list(filename=paths,plot=plots),ggsave)