# fpos: Find a matrix position inside a larger matrix In kit: Data Manipulation Functions Implemented in C

## Description

The function `fpos` returns the locations (row and column index) where a small matrix may be found in a larger matrix. The function also works with vectors.

## Usage

 `1` ``` fpos(needle, haystack, all=TRUE, overlap=TRUE) ```

## Arguments

 `needle` A matrix or vector to search for in the larger matrix or vector `haystack`. Note that the `needle` dimensions (row and column size) must be smaller than the `haystack` diemsions. `haystack` A matrix or vector to look into. `all` A logical value to indicate whether to return all occurences (`TRUE`) or only the first one (`FALSE`). Default value is `TRUE`. `overlap` A logical value to indicate whether to allow the small matrix occurences to overlap or not. Default value is `TRUE`.

## Value

A two columns matrix that contains the position or index where the small matrix (needle) can be found in the larger matrix. The first column refers to rows and the second to columns. In case both the needle and haystack are vectors, a vector is returned.

Morgan Jacob

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34``` ```# Example 1: find a matrix inside a larger one big_matrix = matrix(c(1:30), nrow = 10) small_matrix = matrix(c(14, 15, 24, 25), nrow = 2) fpos(small_matrix, big_matrix) # Example 2: find a vector inside a larger one fpos(14:15, 1:30) # Example 3: big_matrix = matrix(c(1:5), nrow = 10, ncol = 5) small_matrix = matrix(c(2:3), nrow = 2, ncol = 2) # return all occurences fpos(small_matrix, big_matrix) # return only the first fpos(small_matrix, big_matrix, all = FALSE) # return non overlapping occurences fpos(small_matrix, big_matrix, overlap = FALSE) # Benchmarks # ---------- # x = matrix(1:5, nrow=1e4, ncol=5e3) # 191Mb # microbenchmark::microbenchmark( # fpos=kit::fpos(1L, x), # which=which(x==1L, arr.ind=TRUE), # times=10L # ) # Unit: milliseconds # expr min lq mean median uq max neval # fpos 202 206 220 221 231 241 10 # which 612 637 667 653 705 724 10 ```

kit documentation built on March 9, 2021, 5:12 p.m.