annotation in highchart doesn't work as expected - r

Question

I was using Highchart to plot some time series and wanted to add some annotation to the plot to highlight some key points. I knew putting the cursor on the graph can pop up the context, however, some automatic graph generation is needed and hence annotating is the best approach.
And I did that, with the last line in the code below. However, the effect is not what I expected. The text was located at the bottom left corner, not located at the right horizontal position yet the vertical position is right. The time series are created using xts library, which means the horizontal axis is simply the date data structure, nothing fancy. xValue is specified as the 900th element of all the time points which have a total length of 1018, so the 900th time point must be in the second half of the graph.
Anyone knows how I can put the annotation at the right location? Many thanks.
hc <- highchart(type = "stock") %>%
hc_title(text = "Some time series") %>%
hc_add_series(x, color='green', name="x", showInLegend = TRUE) %>%
hc_add_series(y, color='red', name="y", showInLegend = TRUE) %>%
hc_add_series(z, color='blue', name="z", showInLegend = TRUE) %>%
hc_navigator(enabled=FALSE) %>%
hc_scrollbar(enabled=FALSE) %>%
hc_legend(enabled=TRUE, layout="horizontal") %>%
hc_annotations(list(enabledButtons=FALSE, xValue = index(x)[900], yValue = -5, title =list(text = "Hello world! How can I make this work!")))
hc
The data can be roughly generated using the following script:
dt <- seq(as.Date("2014/1/30"), as.Date("2018/2/6"), "days")
dt <- dt[!weekdays(dt) %in% c("Saturday", "Sunday")]
n <- length(dt)
x <- xts(rnorm(n), order.by=dt)
y <- xts(rnorm(n), order.by=dt)
z <- xts(rnorm(n), order.by=dt)

Answer 1

Let's star with the #kamil-kulig example, this will be a little out of R world but I want to give some justification if you don't mind.
If we see annotations options is not a object but a list of object(s), so in highcharter is implemented the hc_add_annotation function.
Now, you are using a old version of highcharter. Highcharter devlopment version is using v6 of highchartsJS which made some changes: before the annotations.js was a pluging now is included as a module with some changes in the names of arguments.
Example I: Simple
The example by Kamil Kulig is replicated doing:
highchart(type = "stock") %>%
hc_add_annotation(
labelOptions = list(
backgroundColor = 'rgba(255,255,255,0.5)',
verticalAlign = 'top',
y = 15
),
labels = list(
list(
point = list(
xAxis = 0,
yAxis = 0,
x = datetime_to_timestamp(as.Date("2017/01/02")),
y = 1.5
),
text = "Some annotation"
)
)
) %>%
hc_xAxis(
minRange = 1
) %>%
hc_add_series(
pointStart = start,
pointInterval = day,
data = c(3, 4, 1)
)
Example II: With your data
Be careful in the way you add the x position. Highcharter include a datetime_to_timestamp function to convert a date into a epoch/timestap which is required for highcharts.
library(xts)
dt <- seq(as.Date("2014/1/30"), as.Date("2018/2/6"), "days")
dt <- dt[!weekdays(dt) %in% c("Saturday", "Sunday")]
n <- length(dt)
x <- xts(rnorm(n), order.by=dt)
y <- xts(rnorm(n), order.by=dt)
z <- xts(rnorm(n), order.by=dt)
highchart(type = "stock") %>%
hc_title(text = "Some time series") %>%
hc_add_series(x, color='green', name="x", showInLegend = TRUE) %>%
hc_add_series(y, color='red', name="y", showInLegend = TRUE) %>%
hc_add_series(z, color='blue', name="z", showInLegend = TRUE) %>%
hc_navigator(enabled=FALSE) %>%
hc_scrollbar(enabled=FALSE) %>%
hc_legend(enabled=TRUE, layout="horizontal") %>%
hc_add_annotation(
labels = list(
list(
point = list(
xAxis = 0,
yAxis = 0,
x = datetime_to_timestamp(as.Date(index(x)[900])),
y = 1
),
text = "Hello world! How can I make this work!"
)
)
)