R: Plot function adding step function to data

Question

I am trying to plot yearly averages for data that I have for three locations. I have used the plot() function regularly and never had a problem like this before. For some reason, every time I plot this data, it adds a step-like style to the first locations data. I have tried to change "type = " to every possible alternative and it seems to just ignore it. I have also tried to set type = "n" and then add the data with points(), and the step-like style to the first set of data is still there.

Here is the data set that I have used:

OrganicsRemoval <- data.frame(Year = c("1995", "1996", "1997", "1998", "1999", "2000", "2001", "2002", "2003", "2004", 
                                   "2005", "2006", "2007", "2008", "2009", "2010", "2011", "2012", "2013", "2014", 
                                   "2015", "2016"),
                          x = c(22,28,20,30,34,31,33,45,42,43,38,50,47,50,50,47,46,44,48,55,57,50),
                          y = c(18,23,25,16,23,24,24,31,36,39,36,42,39,40,42,46,40,42,40,42,44,42),
                          z = c(15,21,22,16,36,33,31,39,38,39,39,46,42,46,45,43,43,44,42,44,45,41))

Here is the code I am using to plot the data:

par(mfrow = c(1,1))
plot(x = OrganicsRemoval$Year, y = OrganicsRemoval$x, type = "n", main = "TOC Percent Removal",
 ylab = "TOC Percent Removal", xlab = "Year", ylim = c(0,65))
points(x = OrganicsRemoval$Year, y = OrganicsRemoval$x, type = "b", col = "red")
points(x = OrganicsRemoval$Year, y = OrganicsRemoval$z, type = "b", col = "blue")
points(x = OrganicsRemoval$Year, y = OrganicsRemoval$y, type = "b", col = "black")
legend("topright", legend = c("x", "z", "y"), col = c("red", "blue", "black"), lwd = 1)

Here is what is output: Output Plot

I would greatly appreciate any help I can get to get rid of those step-like format. Thanks!

Answer 1

When casting OrganicsRemoval$Year as numeric the plot looks correct.

When creating a data frame and not using stringsAsFactors = FALSE string becomes factor. I assume that this caused the trouble. The 'step-like' things appear already in the initial plot statement when not casting as numeric.

plot(x = as.numeric(OrganicsRemoval$Year), y = OrganicsRemoval$x, type = "n", main = "TOC Percent Removal",
 ylab = "TOC Percent Removal", xlab = "Year", ylim = c(0,65))

points(x = OrganicsRemoval$Year, y = OrganicsRemoval$x, type = "b", col = "red")
points(x = OrganicsRemoval$Year, y = OrganicsRemoval$z, type = "b", col = "blue")
points(x = OrganicsRemoval$Year, y = OrganicsRemoval$y, type = "b", col = "black")
legend("topright", legend = c("x", "z", "y"), col = c("red", "blue", "black"), lwd = 1)

Alternatively, you can, as mentioned above, use stringsAsFactors = FALSE when you create the data frame.