listCrawler {crank}

Descend a list, applying a function to each element.

Description

Descend a possibly nested list, seeking the element that has the extreme value of a function.

Usage

 listCrawler(x,FUN=NULL,maxval=TRUE,
  retval=list(indx=vector("numeric",0),element=NULL,value=NA))

Arguments

x

The object that will be the first argument of ‘⁠FUN⁠’, or a possibly nested list of such objects.

FUN

A function that can accept ‘⁠x⁠’ as its first argument.

maxval

Whether to look for maximal (TRUE) or minimal (FALSE) values of the function ‘⁠FUN⁠’.

retval

The list that is eventually returned.

Details

‘⁠listCrawler⁠’ descends the list structure of ‘⁠x⁠’ applying ‘⁠FUN⁠’ to any non-list elements it encounters. If the value of ‘⁠FUN⁠’ is larger or smaller than the current extremum (depending upon the value of ‘⁠maxval⁠’), the new value becomes the current extremum. The default value of ‘⁠FUN⁠’ just takes the value of the elements.

Value

A list containing:

indx

the indices of the element producing the extreme value of ‘⁠FUN⁠’.

element

The element that produced the extremum.

value

The extreme value of ‘⁠FUN⁠’.

Author(s)

Jim Lemon

See Also

list, listBuilder

Examples

 # a simple example using the square root function
 testlist<-list(list(9,16),list(25,list(36,49)))
 # first get the default maximum
 listCrawler(testlist,sqrt)
 # then the minimum
 listCrawler(testlist,sqrt,maxval=FALSE)