Loop over number preceded by underscore symbol in R - r

Question

I apologize in advance but I did not find what I need in previous topic-related posts.
Suppose that I have the following data. "bchain" is a dataframe of 2192 observations. The column "Date" contains dates from 2011/01/01 to 2016/12/31. The column "Value" contains daily exchange rates.
>bchain
Date Value
1 2011-01-01 0.299998
2 2011-01-02 0.299996
3 2011-01-03 0.299998
4 2011-01-04 0.299899
5 2011-01-05 0.298998
6 2011-01-06 0.299000
7 2011-01-07 0.322000
8 2011-01-08 0.322898
. ....... .......
What I want to do is to visualize the exchange rates year by year in separate plots and save the six graphs on my desktop by using a "for" loop. Consider this simple following pseudo-code which I built around this post content:
https://www.r-bloggers.com/automatically-save-your-plots-to-a-folder/
PSEUDO-CODE:
Date_2011=bchain[1:365,1]
Date_2012=bchain[366:731,1]
Date_2013=bchain[732:1096,1]
Date_2014=bchain[1097:1461,1]
Date_2015=bchain[1462:1826,1]
Date_2016=bchain[1827:2192,1]
bchain_2011=bchain[1:365,2]
bchain_2012=bchain[366:731,2]
bchain_2013=bchain[732:1096,2]
bchain_2014=bchain[1097:1461,2]
bchain_2015=bchain[1462:1826,2]
bchain_2016=bchain[1827:2192,2]
years=2011:2016
for(i in years){
mypath = file.path("C:/Users/toshiba1/Desktop",paste("myplot_", years[i], ".jpg", sep = ""))
jpeg(file=mypath)
mytitle = paste("my title is", years[i])
plot(Date_[i],bchain_[i], main = mytitle)
dev.off()
}
Then I get the following error message: object "Date_" not found. I suspect that the problem is that the above loop does not recognize the numbers which come after the underscore sign. So, any suggestion?
Thank you in advance.

Answer 1

Here is another approach avoiding the need to make the year-specific data frames. I used the lubridate package to extract the year from the date values, generated a data.frame of that year, and plotted those data. As #Konrad also pointed out, the way in which you call some of the objects is giving you issues - I cleaned up some of those in your paste statements below.
library(lubridate)
# Create toy data to plot
bchain <- data.frame(Date = seq.Date(from = as.Date("2011-01-01"), to = as.Date("2016-12-31"),
by = 1),
Value = runif(2192, 0, 1))
years <- 2011:2016
for(i in years){
# Create dataset of just data to plot
bchain_plot <- bchain[year(bchain$Date) == i, ]
# Edited file name w/i jpeg call and fixed paste statement
jpeg(filename=paste0("C:/Users/toshiba1/Desktop/myplot_", i, ".jpg"))
# Plot data w/ title included in plot call
plot(bchain_plot$Date, bchain_plot$Value, main = paste("my title is", i))
dev.off()
}

Answer 2

You should call your object properly one approach may involve making use of get on the lines:
# Now plot data number i
x <- get(paste("Date", i, sep = "_"))
# Plot
plot(x)
or simply by nesting:
plot(get(paste("Date", i, sep = "_")))
To test it, see what happens if you type Date_[i] in R console? Are you getting the object you want to pass to the plot function? Arrive at the desired object via get or any other mechanism that suits you and then pass it to the plotting function.
I reckon that you want to iterate through your objects - you need i not [i]. Type [i] in the R console and see what happens.