save_ts: Save time series plots
In leonawicz/mapmate: Make Still Image Sequences For Data Animations

Description Usage Arguments Details Value Examples

Save a time series plot to disk intended to be part of a as a still image sequence of a growing time series.

save_ts(data, x, y, id, cap, dir = ".", col = "black", xlm, ylm,
  axes.only = FALSE, axes.space = TRUE, file = "Rplot",
  png.args = list(width = 1920, height = 1080, res = 300, bg = "transparent"),
  save.plot = TRUE, return.plot = FALSE, overwrite = FALSE,
  num.format = 4)

`data`	data frame containing the `x` and `y` plotting variables.
`x`	character, the column name in `data` for the variable plotted along the x axis.
`y`	character, the column name in `data` for the variable plotted along the y axis.
`id`	character, column name referring to column of `data` representing frame sequence integer IDs.
`cap`	time index/frame ID used to subset `data`. The rows of data retained are all those where `p <= cap`, where `p` represents the frame ID values in column `id`. Defaults to all data if missing.
`dir`	png output directory. Defaults to working directory.
`col`	color of the time series line or the axes lines, ticks, and text. Defaults to black.
`xlm`	x axis limits.
`ylm`	y axis limits.
`axes.only`	only plot axis information, no data. Defaults to `FALSE`.
`axes.space`	if `axes.only=TRUE`, leave room for x and y axes in plot window when `axes.space=TRUE`. Remove this marginal area so that data are plotted over the full canvas when `axes.space=FALSE`. Defaults to `TRUE`. Ignored when `axes.only=TRUE` because of the explicit intent to draw axes.
`file`	character, output filename pattern preceeding the image sequence numbering and file extension. Defaults to `"Rplot"`.
`png.args`	a list of arguments passed to `png`.
`save.plot`	save the plot to disk. Defaults to `TRUE`. Typically only set to `FALSE` for demonstrations and testing.
`return.plot`	return the ggplot object. Defaults to `FALSE`. Only intended for single-plot demonstrations and testing, not for still image sequence automation.
`overwrite`	logical, overwrite existing files. Defaults to `FALSE`. If file exists and `return.plot=TRUE` the plot is still returned. Otherwise returns `NULL`. This is a frame by frame check on each file. File writing is simply skipped for existing files when `overwrite=FALSE`. No error or warning is thrown.
`num.format`	number of digits including any leading zeros for image sequence frame numbering. Defaults to 4, i.e. `0001, 0002, ...`.

For id column frame ID values i, cap subsets data to rows where i <= cap. Sequential application of save_ts should involve iterating cap over the values i. A data frame passed to save_map need not be subset based on the current frame ID in advance so providing cap values is important. See example.

When calling save_ts iteratively from the save_seq wrapper function, save_ts is applied over a list of sequentially subsetted data frames based on the frame IDs. In this case, specifying cap is not needed and an error will be thrown if provided.

Fixed axis limits must be established in advance by computing the max range or other desired range for the x and y variables that are to be plotted.

usually returns NULL after writing file to disk. May return a ggplot object with or without the file writing side effect.

## Not run: 
library(dplyr)
library(purrr)
data(annualtemps)
temps <- mutate(annualtemps, frameID = Year - min(Year) + 1) %>%
  group_by(Year, frameID) %>% summarise(z=mean(z))
xlm <- range(temps$Year)
ylm <- range(temps$z)

# should specify a dir or set working dir for file output
# consider running over a smaller subset of frame IDs
walk(temps$frameID, ~save_ts(temps, x="Year", y="z", id="frameID",
  cap=.x, col="blue", xlm=xlm, ylm=ylm))

## End(Not run)