Initialize Spirals by Special Data Types

Work with date/time object

For time series data, values on x-axis are time points in a certain unit, e.g. days, or hours, and are linearly distributed along the axis. To map time series data to the spiral, internally a simple conversion is applied. Assume the first time point is t1 and the last time point is t2, the number of time points is n = t2 - t1 which is the time difference between the two. If we take [0, 1] for the first time point, [1, 2] for the second time point, and [n-1, n] for the last time point, then internally the spiral is initialized with xlim = c(0, n) and a time point d is converted to the internal numeric value by d - d1 + 0.5.

The unit of time point can be set via the argument unit_on_axis and the unit of the period can be set via the argument period, e.g. unit_on_axis = "days" and period = "years". unit_on_aixs can be set as one of "days", "months", "weeks", "hours", "mins" and "secs". And there are also corresponding values for period. If these two arguments are not set, they are guessed from xlim automatically.

In the following examples, also note the default value of polar_lines_by is also different for different period. E.g. there are 12 polar lines for years (12 months), 7 polar lines for weeks (7 weekdays), 24 polar lines for days (24 hours).

spiral_initialize_by_time(xlim = c("2014-01-01", "2021-06-17"))

## 'unit_to_axis' is set to 'days'.
## 'period' is set to 'years'.

spiral_track(height = 0.6)
spiral_axis()

spiral_initialize_by_time(xlim = c("2021-01-01 00:00:00", "2021-01-05 00:00:00"))

## 'unit_to_axis' is set to 'mins'.
## 'period' is set to 'days'.

spiral_track(height = 0.6)
spiral_axis()

spiral_initialize_by_time(xlim = c("2021-01-01 00:00:00", "2021-01-01 00:10:00"),
    unit_on_axis = "secs", period = "mins")
spiral_track(height = 0.6)
spiral_axis()

As shown in previous examples, the values for xlim should be a time/date object or their character forms that can be converted to the time/date object. Later when adding graphics, the time/date objects or their character forms can also be used as the x-locations for the low-level graphics functions. For example:

spiral_points("2021-01-01", 0.5)

Argument at can be set to a vector of times to control the breaks on the axis. In the next example, I set the time interval to every two hours.

spiral_initialize_by_time(xlim = c("2021-01-01 00:00:00", "2021-01-05 00:00:00"))

## 'unit_to_axis' is set to 'mins'.
## 'period' is set to 'days'.

spiral_track(height = 0.6)

library(lubridate)
# `by` is measured in seconds
at = seq(as.POSIXlt("2021-01-01 00:00:00"), as.POSIXlt("2021-01-05 00:00:00"), by = 2*60*60)
spiral_axis(at = at)

In the last example of this section, I let the spiral go clockwisely and put 0/12 o’clock on the top of each loop (simply done by setting clockwise = TRUE) and each loop corresponds to 12 hours:

spiral_initialize_by_time(xlim = c("2021-01-01 00:00:00", "2021-01-03 00:00:00"),
    start = 360 + 90, period_per_loop = 0.5, clockwise = TRUE)

## 'unit_to_axis' is set to 'mins'.
## 'period' is set to 'days'.

spiral_track(height = 0.6)
at = seq(as.POSIXlt("2021-01-01 00:00:00"), as.POSIXlt("2021-01-05 00:00:00"), by = 2*60*60)
spiral_axis(at = at)

When each loop corresponds to a year and units on axis are days, maybe you have already seen the messages in the previous examples, by default, each loop actually corresponds to only 52 weeks (364 days) and the remaining 1 or 2 days will be added and accumulated to the next year. This might be a problem when there are many loops (many years). In the following left plot where we visualize 10 years, the total accumuated years result in about 15 degrees exceeding the full circle. The function spiral_initialize_by_time() allows to set an argument normalize_year = TRUE so that each loop is perfectly a year. But users need to be cautious that now it is not easy to correspond weekdays between years because they are not perfectly aligned.

# the left plot
spiral_initialize_by_time(xlim = c("2010-01-01", "2019-12-31"))
spiral_track()
for(i in 0:9) {
    # years() is from lubridate package
    spiral_text(as.POSIXlt("2010-01-01") + years(i), 0.5, 2010 + i, facing = "inside")
}

# the right plot
spiral_initialize_by_time(xlim = c("2010-01-01", "2019-12-31"),
    normalize_year = TRUE)
spiral_track()
for(i in 0:9) {
    spiral_text(as.POSIXlt("2010-01-01") + years(i), 0.5, 2010 + i, facing = "inside")
}

## 'unit_to_axis' is set to 'days'.
## 'period' is set to 'years'.

## 'unit_to_axis' is set to 'days'.
## 'period' is set to 'years'.

Last, when each loop corresponds to a year and units on axis are days, and when normalize_year is set to TRUE, the background sectors partitioned by dashed radical lines actually correspond to the proportion of month days in a year, i.e., the width of Feburary is the smallest.

spiral_initialize_by_time(xlim = c("2010-01-01", "2014-12-31"), normalize_year = TRUE)

## 'unit_to_axis' is set to 'days'.
## 'period' is set to 'years'.

spiral_track()
for(i in 0:11) {
    d = as.POSIXlt("2014-01-15") + months(i)
    spiral_text(d, 1.5, month.name[month(d)], gp = gpar(fontsize = 8), 
        facing = "inside", nice_facing = TRUE)
}

Work with genomic coordinates

Genomic data can be represented as a data frame (e.g. in bed format), or as a GRanges object. To initialize the spiral for genomic data visualization, the data on x-axis corresponds to the genomic coordinates. The spiral with genomic data can be initialized by the function spiral_initialize_by_gcoor(). The genomic coordinates are linear numeric values, thus, spiral_initialize_by_gcoor() is basically the same as spiral_initialize(). The only difference is the axis labels are automatically formatted for genomic coordinates.

Also since normally there are no periodic patterns for genomc data, scale_by is by default set to "curve_length".

spiral_initialize_by_gcoor(xlim = c(2e6, 8e6))  # 2MB to 8MB
spiral_track(height = 0.6)
spiral_axis()
spiral_points(x = runif(500, min = 2e6, max = 8e6), runif(500), pch = 16, gp = gpar(col = 2))