#  File src/library/utils/R/modifyList.R
#  Part of the R package, http://www.R-project.org
#
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#
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#  it under the terms of the GNU General Public License as published by
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#  This program is distributed in the hope that it will be useful,
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### Originates from Deepayan Sarkar as  updateList() from 'lattice' package

modifyList <- function(x, val, keep.null = FALSE)
{
    stopifnot(is.list(x), is.list(val))
    xnames <- names(x)
    vnames <- names(val)
    ## Will not update unnamed components.  FIXME: What if names are repeated? Warn?
    vnames <- vnames[vnames != ""]
    if (keep.null) {
        for (v in vnames) {
            x[v] <-
                if (v %in% xnames && is.list(x[[v]]) && is.list(val[[v]]))
                    list(modifyList(x[[v]], val[[v]], keep.null = keep.null))
                else val[v]
        }
    }
    else {
        for (v in vnames) {
            x[[v]] <-
                if (v %in% xnames && is.list(x[[v]]) && is.list(val[[v]]))
                    modifyList(x[[v]], val[[v]], keep.null = keep.null)
                else val[[v]]
        }
    }
    x
}