breakWidth Parameter in Datetime Scales

In datetime scales, the breakWidth parameter accepts a string specifying the interval between breaks, e.g., "2 weeks", "3 months", "12 hours".

%useLatestDescriptors
%use lets-plot

val csvUrl = "https://raw.githubusercontent.com/JetBrains/lets-plot-docs/master/data/economics.csv"
val text = java.net.URL(csvUrl).readText()
val lines = text.trim().split("\n")
val header = lines[0].split(",")
val dateIdx = header.indexOfFirst { it.trim('"') == "date" }
val unemployIdx = header.indexOfFirst { it.trim('"') == "unemploy" }

val start = java.time.LocalDate.of(2007, 1, 1)
val end = java.time.LocalDate.of(2013, 1, 1)

val dates = mutableListOf<Long>()
val unemploy = mutableListOf<Double>()

for (line in lines.drop(1)) {
    val cols = line.split(",")
    val dateStr = cols.getOrNull(dateIdx)?.trim()?.trim('"') ?: continue
    val date = runCatching { java.time.LocalDate.parse(dateStr) }.getOrNull() ?: continue
    if (!date.isBefore(start) && date.isBefore(end)) {
        val epochMs = date.atStartOfDay(java.time.ZoneOffset.UTC).toInstant().toEpochMilli()
        dates.add(epochMs)
        unemploy.add(cols[unemployIdx].trim().toDouble())
    }
}

val economics = mapOf("date" to dates, "unemploy" to unemploy)
println("Loaded ${dates.size} rows")

Loaded 72 rows

// A datetime scale with auto-selected breaks
letsPlot(economics) { x = "date"; y = "unemploy" } +
    geomLine(size = 5, alpha = 0.5, color = "teal") +
    scaleXDateTime() +
    themeClassic() +
    ggsize(800, 300)

letsPlot(economics) { x = "date"; y = "unemploy" } +
    geomLine(size = 5, alpha = 0.5, color = "teal") +
    scaleXDateTime(
        breakWidth = "3 months",      // breaks every 3 months
        format = "%b '%y"
    ) +
    themeClassic() +
    ggsize(800, 300)