Shift transform ^0.6.12
The shift transform is a specialized map transform that derives an output x1 channel by shifting the x channel; it can be used with the difference mark to show change over time. For example, the chart below shows the price of Apple stock. The green region shows when the price went up over the given interval, while the blue region shows when the price went down.
Plot.differenceY(aapl, Plot.shiftX("365 days", {x: "Date", y: "Close"})).plot({y: {grid: true}})When looking at year-over-year growth, the chart is mostly green, implying that you would make a profit by holding Apple stock for a year. However, if you bought in 2015 and sold in 2016, you would likely have lost money. Try adjusting the slider to a shorter or longer interval: how does that affect the typical return?
shiftX(interval, options)
Plot.shiftX("7 days", {x: "Date", y: "Close"})Derives an x1 channel from the input x channel by shifting values by the given interval. The interval may be specified as: a name (second, minute, hour, day, week, month, quarter, half, year, monday, tuesday, wednesday, thursday, friday, saturday, sunday) with an optional number and sign (e.g., +3 days or -1 year); or as a number; or as an implementation — such as d3.utcMonth — with interval.floor(value), interval.offset(value), and interval.range(start, stop) methods.
The shiftX also transform aliases the x channel to x2 and applies a domain hint to the x2 channel such that by default the plot shows only the intersection of x1 and x2. For example, if the interval is +1 year, the first year of the data is not shown.