Months displayed incorrectly when using ggplot2

Question

Hi having a problem where March appears twice in my graph but not in my Data.

My data looks like. My data frame is called try1.

    Month                 Year    tcol
   2016-01-01 00:00:00    06      1461.0
   2016-02-01 00:00:00    06      259.5
   2016-03-01 00:00:00    06      191.2
   2016-04-01 01:00:00    06      151.5
   2016-05-01 01:00:00    06      119.6
   2016-06-01 01:00:00    06      1372.5
   2016-07-01 01:00:00    06      954.0
   2016-08-01 01:00:00    06      1784.0
   2016-09-01 01:00:00    06      1369.0
   2016-10-01 01:00:00    06      6077.0
   2016-11-01 00:00:00    06      1638.0
   2016-12-01 00:00:00    06      3308.0

And my code looks like.

ggplot(try1, aes(Month,tcol)) + 
       geom_point(aes(colour = Year),size=2) + 
       geom_line(aes(colour = Year), size=0.73)+
       theme_bw()+
       guides(col = guide_legend(ncol = 2))+
       scale_x_datetime(
                        breaks=date_breaks("1 months"), 
                        labels=date_format("%B"))+
       xlab("")+ #x axis label 
       ylab("Total Coliforms")

The problem is that when I plot my graph March appears twice. And October appears to be left out.

The resulting graph

Thanks for your help.

I can't reproduce the issue. Could you run dput(try1) and copy the result into your question. That will we are working with the same classes of objects. — Benjamin
– Benjamin, Commented Sep 26, 2016 at 12:26
@9Heads, your month labels are off by 1 month; they start with December and end in November). Not quite sure how you accomplished that. :) — Benjamin
– Benjamin, Commented Sep 26, 2016 at 12:31
@Benjamin It was fault of the default time zone which it was taking instead of my system time zone. After the correction Link of the plot — 9Heads
– 9Heads, Commented Sep 26, 2016 at 13:06

Weihuang Wong · Accepted Answer · 2016-09-26 13:20:24Z

I suspect it is a timezone issue. E.g., with this data

structure(list(Month = structure(list(sec = c(0, 0, 0, 0, 0, 
0, 0, 0, 0, 0, 0, 0), min = c(0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 
0L, 0L, 0L, 0L), hour = c(0L, 0L, 0L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 0L, 0L), mday = c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L), mon = 0:11, year = c(116L, 116L, 116L, 116L, 116L, 116L, 
116L, 116L, 116L, 116L, 116L, 116L), wday = c(5L, 1L, 2L, 5L, 
0L, 3L, 5L, 1L, 4L, 6L, 2L, 4L), yday = c(0L, 31L, 60L, 91L, 
121L, 152L, 182L, 213L, 244L, 274L, 305L, 335L), isdst = c(0L, 
0L, 0L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 0L, 0L), zone = c("GMT", 
"GMT", "GMT", "BST", "BST", "BST", "BST", "BST", "BST", "BST", 
"GMT", "GMT"), gmtoff = c(NA_integer_, NA_integer_, NA_integer_, 
NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_, 
NA_integer_, NA_integer_, NA_integer_, NA_integer_)), .Names = c("sec", 
"min", "hour", "mday", "mon", "year", "wday", "yday", "isdst", 
"zone", "gmtoff"), class = c("POSIXlt", "POSIXt"), tzone = c("Europe/London", 
"GMT", "BST")), Year = c(6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 
6L, 6L, 6L), tcol = c(1461, 259.5, 191.2, 151.5, 119.6, 1372.5, 
954, 1784, 1369, 6077, 1638, 3308)), .Names = c("Month", "Year", 
"tcol"), row.names = c(NA, -12L), class = "data.frame")

I can reproduce your chart. Try changing the timezone

attr(try1$Month, "tzone") <- "UTC"

and replot.

Update. I was wondering why changing the timezone to "UTC" works. It turns out that date_format() takes a tz argument that defaults to "UTC". See ?date_format. This means that instead of changing the timezone of Month to "UTC", you can also fix your problem by changing the tz argument in date_format() to whatever the original timezone of Month is, which you can inspect via attr(try1$Month, "tzone").

It's Indeed a timezone issue. I plotted the data above with my system time zone and got the correct graph. Link of the plot

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