Question

I have the following very simple R script which uses zoo to visualize daily numbers on a timeline:

# Small script to plot daily number of added users to database
library(zoo)

data <- read.csv("search_history.csv", header=FALSE)
# last line will be cut because it might be incomplete
zoodata <- data[1:(length(data$V2)-1), ]
series <- zoo(zoodata$V2, zoodata$V1)

par(mar=c(7, 6, 4, 2), 
    lab=c(5, 6, 5), 
    mgp = c(4, 1, 0))

plot(series,
     main="Number of users added to database over time", 
     xlab="Date", 
     ylab="Number of users",
     las=2,
     lwd=2,
     col="red",
     cex.axis=0.7)

Content of search_history.csv:

"2012-12-27","458","4728"
"2012-12-28","239","6766"
"2012-12-29","193","8189"
"2012-12-30","148","7698"
"2012-12-31","137","7370"
"2013-01-01","119","6324"
"2013-01-02","122","7016"
"2013-01-03","115","7986"
"2013-01-04","112","8222"
"2013-01-05","112","6828"
"2013-01-06","124","7318"
"2013-01-07","121","8228"
"2013-01-08","120","8158"
...

I want to visualize the first (V1) and the second column (V2). I basically have two problems: The first and obvious one are the dashed lines at y-Position ~50 and ~450. How can I remove them and why are they even included?

The second problem is the inclusion of 2013-01-26 in the x-Axis. As you can see, I removed the last line of the dataset which contains this data (like an amateur, maybe there is a better way to do this). So the plot should not include the last date. I don’t understand why it even knows about this date since it takes zoodata as input, not data.

Answer 1

Two things: Your strings are being read as factors, and you are indexing your zoo object by a character vector instead of by Dates.

If you include stringsAsFactors=FALSE in your read.csv call and give your zoo object a Date index it will look more like you were expecting.

library(zoo)    
data <- read.csv(text='"2012-12-27","458","4728"
                 "2012-12-28","239","6766"
                 "2012-12-29","193","8189"
                 "2012-12-30","148","7698"
                 "2012-12-31","137","7370"
                 "2013-01-01","119","6324"
                 "2013-01-02","122","7016"
                 "2013-01-03","115","7986"
                 "2013-01-04","112","8222"
                 "2013-01-05","112","6828"
                 "2013-01-06","124","7318"
                 "2013-01-07","121","8228"
                 "2013-01-08","120","8158"', header=FALSE, 
                 stringsAsFactors=FALSE)

zoodata <- data[1:(length(data$V2)-1), ]
series <- zoo(zoodata$V2, as.Date(zoodata$V1))

par(mar=c(7, 6, 4, 2), 
    lab=c(5, 6, 5), 
    mgp = c(4, 1, 0))

plot(series,
     main="Number of users added to database over time", 
     xlab="Date", 
     ylab="Number of users",
     las=2,
     lwd=2,
     col="red",
     cex.axis=0.7)

Which produces: