changes: Change Scores from Numeric Data
In quest: Prepare Questionnaire Data for Analysis

Description Usage Arguments Details Value See Also Examples

changes creates change scores (aka difference scores) from numeric data. It is assumed that the data is already sorted by time such that the first row is earliest in time and the last row is the latest in time. changes is a multivariate version of change that operates on multiple variabes rather than just one.

1	changes(data, vrb.nm, n, undefined = NA, suffix)

`data`	data.frame of data.
`vrb.nm`	character vector of colnames from `data` specifying the variables.
`n`	integer vector with length 1. Specifies how the change score is calculated. If `n` is positive, then the change score is calculated from lead - original; if `n` is negative, then the change score is calculated from original - lag. The magnitude of `n` determines how many rows are shifted for the lead/lag within the calculation. See details of `shifts`.
`undefined`	atomic vector with length 1 (probably makes sense to be the same typeof as `x`). Specifies what to insert for undefined values after the shifting takes place. See details of `shifts`.
`suffix`	character vector of length 1 specifying the string to append to the end of the colnames of the return object. The default depends on the `n` argument: 1) if `n` < 0, then `suffix` = `paste0("_hg", -n)`, 2) if `n` > 0, then `suffix` = `paste0("_hd", +n)`, 3) if `n` = 0, then `suffix` = "".

It is recommended to use L when specifying n to prevent problems with floating point numbers. shifts tries to circumvent this issue by a call to round within shifts if n is not an integer; however that is not a complete fail safe. The problem is that as.integer(n) implicit in shifts truncates rather than rounds. See details of shifts.

data.frame of change scores with colnames specified by paste0(vrb.nm, suffix).

change changes_by change_by shifts

changes(attitude, vrb.nm = names(attitude),
   n = -1L) # use L to prevent problems with floating point numbers
changes(attitude, vrb.nm = names(attitude),
   n = -2L) # can specify any integer up to the length of `x`
changes(attitude, vrb.nm = names(attitude),
   n = +1L) # can specify negative or positive integers
changes(attitude, vrb.nm = names(attitude),
   n = +2L, undefined = -999) # user-specified indefined value
changes(attitude, vrb.nm = names(attitude),
   n = -2L, undefined = -999) # user-specified indefined value
## Not run: 
changes(str2str::d2d(InsectSprays), names(InsectSprays),
  n = 3L) # character vector returns an error

## End(Not run)