locate.fid: Returns the index locations that match vector fid within data...

In gtatters/Thermimage: Thermal Image Analysis

Description

Returns the index locations that match vector fid within data vector. Used mostly to search for magic byte locations in a raw vector, but can be used to search any vector for locations of fid.

Usage

locate.fid(fid, vect, long = TRUE, zeroindex = TRUE)

Arguments

fid	A lookup vector, typically numeric, which can be 1 element long or greater. Typical use is 2 elements long. fid<-c(1,2). This sequence of values will be searched within the data vector, vect.
vect	Data vector of interest, within which fid will be searched.
long	Default is TRUE, will use a slower algorithm. When long=true, any length of fid can be used to search in vector. Computing time also depends on the length of fid. Caution advised when setting long = FALSE. Null values maye be returned.
zeroindex	Whether you wish the returned values to reference 0 as the starting index or 1 as the starting index. Natural byte reading starts at 0, but in R, indexes start at 1, so set zeroindex=FALSE if you using this simply as a vector lookup tool in R. Default is TRUE.

Details

Returns the positions within the data vector where fid is found. Do not use this function if fid is length = 1. Use which(). If length(fid)>1, the elements of fid must be adjacent and in that specific order.

Value

An object of type integer, to be used as an index subset.

Author(s)

Glenn J. Tattersall

See Also

match which

Examples

# Similar to the which or match functions in package::base, except that this returns the 
# index placement where variable fid occurs in data

## Define a vector
s<-c(2,3,42,38,88,33,55,99,32,56,22,48,1,2,3,5,6,7,8,9,10,12,20)
## Define what fid sequence to look for: i.e. what adjacent elements to look for in 
## this order
fid<-c(22,48)
## look for all instances where 22 and 48 occur together, using locate.fid
system.time(where.locate<-locate.fid(fid,s,long=FALSE, zeroindex=FALSE))
where.locate
## verify that locate.fid worked by subsetting s, using where.locate as index
s[where.locate]
system.time(where.locate<-locate.fid(fid,s,long=TRUE, zeroindex=FALSE))
s[where.locate]

## longer algorithm check
### Define a vector of 100000 random numbers from 1 to 100
s<-ceiling(runif(100000, 0, 100))
## Define what fid sequence to look for: i.e. what adjacent elements to look for in 
## this order
fid<-c(22,48)
system.time(where.locate<-locate.fid(fid,s,long=TRUE,zeroindex=FALSE))
where.locate
## verify that locate.fid worked by subsetting s, using where.locate as index
s[where.locate]

gtatters/Thermimage documentation built on Sept. 28, 2021, 2:02 p.m.