lapplI: Improve 'lapply' and 'sapply' with index
In labelmachine: Make Labeling of R Data Sets Easy

Improve base::lapply() and base::sapply() functions by allowing an extra index argument .I to be passed into the function given in FUN. If the function given in FUN has an argument .I then, for each entry of X passed into FUN the corresponding index is passed into argument .I. If the function given in FUN has no argument .I, then lapplI and sapplI are exactly the same as base::lapply() and base::sapply(). Besides this extra feature, there is no difference to base::lapply() and base::sapply().

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lapplI(X, FUN, ...)

sapplI(X, FUN, ..., simplify = TRUE, USE.NAMES = TRUE)

`X`	a vector (atomic or list) or an `expression` object. Other objects (including classed objects) will be coerced by `base::as.list`.
`FUN`	Here comes the great difference to `base::lapply()` and `base::sapply()`. When using `lapplI` and `sapplI`, the function passed into `FUN` may also have an extra argument `.I`. If it does, then for each item of `X` the current item index is passed into argument `.I` of `FUN`. Besides this extra feature, there is no difference to `base::lapply()` and `base::sapply()`.
`...`	optional arguments to `FUN`.
`simplify`	logical or character string; should the result be simplified to a vector, matrix or higher dimensional array if possible? For `sapply` it must be named and not abbreviated. The default value, `TRUE`, returns a vector or matrix if appropriate, whereas if `simplify = "array"` the result may be an `array` of “rank” (=`length(dim(.))`) one higher than the result of `FUN(X[[i]])`.
`USE.NAMES`	logical; if `TRUE` and if `X` is character, use `X` as `names` for the result unless it had names already. Since this argument follows `...` its name cannot be abbreviated.