fit_trajectory: Apply a model fit to an individual's trajectory
In hafen/hbgd: Healthy birth, growth & development

Apply a model fit to an individual's trajectory

1 2	fit_trajectory(dat, fit, xg = NULL, checkpoints = 365 * c(1:2), z_bins = -2)

`dat`	data frame containing variables for one subject to apply a fit to
`fit`	an object returned from `get_fit`
`xg`	grid of x points at which the fit should be evaluated for plotting (if `NULL` it will be set to an equally-spaced grid of 150 points across `x`)
`checkpoints`	x values at which to compute "checkpoints" of the subjects's growth trajectory to compare to other subjects
`z_bins`	a vector indicating binning of z-scores for the subject's trajectory at each checkpoint with respect to the the WHO growth standard

mod <- get_fit(cpp, y_var = "wtkg")
fit <- fit_trajectory(subset(cpp, subjid == 2), mod)
plot(fit$xy$x, fit$xy$y)
lines(fit$fitgrid$x, fit$fitgrid$y)
# there is also a plot method:
plot(fit, x_range = c(0, 2560))

# we can fit the z-scores instead
mod2 <- get_fit(cpp, y_var = "waz")
fit2 <- fit_trajectory(subset(cpp, subjid == 2), mod2)
plot(fit2$xy$x, fit2$xy$z)
lines(fit2$fitgrid$x, fit2$fitgrid$z)
# using the plot method
plot(fit2, x_range = c(0, 2560), center = TRUE)