rlist (version 0.4.6.1)

list.search: Search a list recusively by an expression

Description

Search a list recusively by an expression

Usage

list.search(.data, expr, classes = "ANY", n, unlist = FALSE)

Arguments

.data

A list or vector

expr

a lambda expression

classes

a character vector of class names that restrict the search. By default, the range is unrestricted (ANY).

n

the maximal number of vectors to return

unlist

logical Should the result be unlisted?

Details

list.search evaluates an expression (expr) recursively along a list (.data).

If the expression results in a single-valued logical vector and its value is TRUE, the whole vector will be collected If it results in multi-valued or non-logical vector, the non-NA values resulted from the expression will be collected.

To search whole vectors that meet certain condition, specify the expression that returns a single logical value.

To search the specific values within the vectors, use subsetting in the expression, that is, .[cond] or lambda expression like x -> x[cond] where cond is a logical vector used to select the elements in the vector.

Examples

# NOT RUN {
# Exact search

x <- list(p1 = list(type='A',score=c(c1=9)),
       p2 = list(type=c('A','B'),score=c(c1=8,c2=9)),
       p3 = list(type=c('B','C'),score=c(c1=9,c2=7)),
       p4 = list(type=c('B','C'),score=c(c1=8,c2=NA)))

## Search exact values
list.search(x, identical(., 'A'))
list.search(x, identical(., c('A','B')))
list.search(x, identical(., c(9,7)))
list.search(x, identical(., c(c1=9,c2=7)))

## Search all equal values
list.search(x, all(. == 9))
list.search(x, all(. == c(8,9)))
list.search(x, all(. == c(8,9), na.rm = TRUE))

## Search any equal values
list.search(x, any(. == 9))
list.search(x, any(. == c(8,9)))

# Fuzzy search

data <- list(
  p1 = list(name='Ken',age=24),
  p2 = list(name='Kent',age=26),
  p3 = list(name='Sam',age=24),
  p4 = list(name='Keynes',age=30),
  p5 = list(name='Kwen',age=31)
)

list.search(data, grepl('^K\\w+n$', .), 'character')

# }
# NOT RUN {
library(stringdist)
list.search(data, stringdist(., 'Ken') <= 1, 'character')
list.search(data, stringdist(., 'Man') <= 2, 'character')
list.search(data, stringdist(., 'Man') > 2, 'character')
# }
# NOT RUN {
data <- list(
  p1 = list(name=c('Ken', 'Ren'),age=24),
  p2 = list(name=c('Kent', 'Potter'),age=26),
  p3 = list(name=c('Sam', 'Lee'),age=24),
  p4 = list(name=c('Keynes', 'Bond'),age=30),
  p5 = list(name=c('Kwen', 'Hu'),age=31))

list.search(data, .[grepl('e', .)], 'character')

# }
# NOT RUN {
list.search(data, all(stringdist(., 'Ken') <= 1), 'character')
list.search(data, any(stringdist(., 'Ken') > 1), 'character')
# }