Package 'grr'

Extract/return parts of objects

Description

Alternative to built-in Extract or [. Allows for extraction operations that are ambivalent to the data type of the object. For example, extract(x,i) will work on lists, vectors, data frames, matrices, etc.

Usage

extract(x, i = NULL, j = NULL)

Arguments

x	object from which to extract elements
i, j	indices specifying elements to extract. Can be numeric, character, or logical vectors.

Details

Extraction is 2-100x faster on data frames than with the built in operation - but does not preserve row names.

Examples

#Typically about twice as fast on normal subselections
orders<-data.frame(orderNum=1:1e5,
 sku=sample(1e3, 1e5, TRUE),
 customer=sample(1e4,1e5,TRUE))
a<-sample(1e5,1e4)
system.time(b<-orders[a,])
system.time(c<-extract(orders,a))
rownames(b)<-NULL
rownames(c)<-NULL
identical(b,c)

#Speedup increases to 50-100x with oversampling 
a<-sample(1e5,1e6,TRUE)
system.time(b<-orders[a,])
system.time(c<-extract(orders,a))
rownames(b)<-NULL
rownames(c)<-NULL
identical(b,c)

#Can create function calls that work for multiple data types
alist<-as.list(1:50)
avector<-1:50
extract(alist,1:5)
extract(avector,1:5)
extract(orders,1:5)#'

## Not run: 
orders<-data.frame(orderNum=as.character(sample(1e5, 1e6, TRUE)),
 sku=sample(1e3, 1e6, TRUE),
 customer=sample(1e4,1e6,TRUE))
system.time(a<-sample(1e6,1e7,TRUE))
system.time(b<-orders[a,])
system.time(c<-extract(orders,a))

## End(Not run)

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Alternative Implementations of Base R Functions

Description

Alternative implementations of some base R functions, including sort, order, and match. Functions are simplified but can be faster or have other advantages. See the documentation of individual functions for details and benchmarks.

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Value Matching

Description

Returns a lookup table or list of the positions of ALL matches of its first argument in its second and vice versa. Similar to match, though that function only returns the first match.

Usage

matches(x, y, all.x = TRUE, all.y = TRUE, list = FALSE, indexes = TRUE,
  nomatch = NA)

Arguments

x	vector. The values to be matched. Long vectors are not currently supported.
y	vector. The values to be matched. Long vectors are not currently supported.
all.x	logical; if TRUE, then each value in x will be included even if it has no matching values in y
all.y	logical; if TRUE, then each value in y will be included even if it has no matching values in x
list	logical. If TRUE, the result will be returned as a list of vectors, each vector being the matching values in y. If FALSE, result is returned as a data frame with repeated values for each match.
indexes	logical. Whether to return the indices of the matches or the actual values.
nomatch	the value to be returned in the case when no match is found. If not provided and indexes=TRUE, items with no match will be represented as NA. If set to NULL, items with no match will be set to an index value of length+1. If indexes=FALSE, they will default to NA.

Details

This behavior can be imitated by using joins to create lookup tables, but matches is simpler and faster: usually faster than the best joins in other packages and thousands of times faster than the built in merge.

all.x/all.y correspond to the four types of database joins in the following way:

left

all.x=TRUE, all.y=FALSE

right

all.x=FALSE, all.y=TRUE

inner

all.x=FALSE, all.y=FALSE

full

all.x=TRUE, all.y=TRUE

Note that NA values will match other NA values.

Examples

one<-as.integer(1:10000)
two<-as.integer(sample(1:10000,1e3,TRUE))
system.time(a<-lapply(one, function (x) which(two %in% x)))
system.time(b<-matches(one,two,all.y=FALSE,list=TRUE))

one<-round(runif(1e3),3)
two<-round(runif(1e3),3)
system.time(a<-lapply(one, function (x) which(two %in% x)))
system.time(b<-matches(one,two,all.y=FALSE,list=TRUE))
 
one<-as.character(1:1e5)
two<-as.character(sample(1:1e5,1e5,TRUE))
system.time(b<-matches(one,two,list=FALSE))
system.time(c<-merge(data.frame(key=one),data.frame(key=two),all=TRUE))
 
## Not run: 
one<-as.integer(1:1000000)
two<-as.integer(sample(1:1000000,1e5,TRUE))
system.time(b<-matches(one,two,indexes=FALSE))
if(requireNamespace("dplyr",quietly=TRUE))
 system.time(c<-dplyr::full_join(data.frame(key=one),data.frame(key=two)))
if(require(data.table,quietly=TRUE))
 system.time(d<-merge(data.table(data.frame(key=one))
             ,data.table(data.frame(key=two))
             ,by='key',all=TRUE,allow.cartesian=TRUE))

one<-as.character(1:1000000)
two<-as.character(sample(1:1000000,1e5,TRUE))
system.time(a<-merge(one,two)) #Times out
system.time(b<-matches(one,two,indexes=FALSE))
if(requireNamespace("dplyr",quietly=TRUE))
 system.time(c<-dplyr::full_join(data.frame(key=one),data.frame(key=two)))#'
if(require(data.table,quietly=TRUE))
{
 system.time(d<-merge(data.table(data.frame(key=one))
             ,data.table(data.frame(key=two))
             ,by='key',all=TRUE,allow.cartesian=TRUE))
 identical(b[,1],as.character(d$key))
}

## End(Not run)

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Ordering vectors

Description

Simplified implementation of order. For large vectors, typically is about 3x faster for numbers and 20x faster for characters.

Usage

order2(x)

Arguments

x	a vector of class numeric, integer, character, factor, or logical. Long vectors are not supported.

Examples

chars<-as.character(sample(1e3,1e4,TRUE))
system.time(a<-order(chars))
system.time(b<-order2(chars))
identical(chars[a],chars[b])

ints<-as.integer(sample(1e3,1e4,TRUE))
system.time(a<-order(ints))
system.time(b<-order2(ints))
identical(ints[a],ints[b])

nums<-runif(1e4)
system.time(a<-order(nums))
system.time(b<-order2(nums))
identical(nums[a],nums[b])

logs<-as.logical(sample(0:1,1e6,TRUE))
system.time(a<-order(logs))
system.time(b<-order2(logs))
identical(logs[a],logs[b])

facts<-as.factor(as.character(sample(1e3,1e4,TRUE)))
system.time(a<-order(facts))
system.time(b<-order2(facts))
identical(facts[a],facts[b])

#How are special values like NA and Inf handled?
#For numerics, values sort intuitively, with the important note that NA and
#NaN will come after all real numbers but before Inf.
(function (x) x[order2(x)])(c(1,2,NA,NaN,Inf,-Inf))
#For characters, values sort correctly with NA at the end.
(function (x) x[order2(x)])(c('C','B',NA,'A'))
#For factors, values sort correctly with NA at the end.
(function (x) x[order2(x)])(as.factor(c('C','B',NA,'A')))

## Not run: 
chars<-as.character(sample(1e5,1e6,TRUE))
system.time(a<-order(chars))
system.time(b<-order2(chars)) 

ints<-as.integer(sample(1e5,1e6,TRUE))
system.time(result<-order(ints))
system.time(result<-order2(ints))

nums<-runif(1e6)
system.time(result<-order(nums))
system.time(result<-order2(nums)) 

logs<-as.logical(sample(0:1,1e7,TRUE))
system.time(result<-order(logs))
system.time(result<-order2(logs))

facts<-as.factor(as.character(sample(1e5,1e6,TRUE)))
system.time(a<-order(facts))
system.time(b<-order2(facts))
identical(facts[a],facts[b])



## End(Not run)

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Sorting vectors

Description

Simplified implementation of sort. For large vectors, typically is about 2x faster for numbers and 20x faster for characters and factors.

Usage

sort2(x)

Arguments

x	a vector of class numeric, integer, character, factor, or logical. Long vectors are not supported.

Examples

chars<-as.character(sample(1e3,1e4,TRUE))
system.time(a<-sort(chars))
system.time(b<-sort2(chars))
identical(a,b)  
 
ints<-as.integer(sample(1e3,1e4,TRUE))
system.time(a<-sort(ints))
system.time(b<-sort2(ints))
identical(a,b)
 
nums<-runif(1e4)
system.time(a<-sort(nums))
system.time(b<-sort2(nums))
identical(a,b)

logs<-as.logical(sample(0:1,1e6,TRUE))
system.time(result<-sort(logs))
system.time(result<-sort2(logs))

facts<-as.factor(as.character(sample(1e3,1e4,TRUE)))
system.time(a<-sort(facts))
system.time(b<-sort2(facts))
identical(a,b)

#How are special values like NA and Inf handled?
#For numerics, values sort intuitively, with the important note that NA and
#NaN will come after all real numbers but before Inf.
sort2(c(1,2,NA,NaN,Inf,-Inf))
#For characters, values sort correctly with NA at the end.
sort2(c('C','B',NA,'A'))
#For factors, values sort correctly with NA at the beginning.
sort2(as.factor(c('C','B',NA,'A')))

## Not run: 
chars<-as.character(sample(1e5,1e6,TRUE))
system.time(a<-sort(chars))
system.time(b<-sort2(chars))

ints<-as.integer(sample(1e5,1e6,TRUE))
system.time(result<-sort(ints))
system.time(result<-sort2(ints))

nums<-runif(1e6)
system.time(result<-sort(nums))
system.time(result<-sort2(nums))

logs<-as.logical(sample(0:1,1e7,TRUE))
system.time(result<-sort(logs))
system.time(result<-sort2(logs))

facts<-as.factor(as.character(sample(1e5,1e6,TRUE)))
system.time(a<-sort(facts))
system.time(b<-sort2(facts))

## End(Not run)

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