select_flows: Flow selection

In rCarto/flows: Selections on Flow Matrices, Statistics on Selected Flows, Map and Graph Visualisations

Flow selection

Description

Flow selection from origins.

Usage

select_flows(mat, method = "nfirst", ties = "first", global = FALSE, k, w)

Arguments

mat	A square matrix of flows.
method	A method of flow selection, one of "dominant", "nfirst", "xfirst" or "xsumfirst": dominant selects the dominant flows (see Details) nfirst selects the k first flows from origins, xfirst selects flows greater than k, xsumfirst selects as many flows as necessary for each origin so that their sum is at least equal to k. If k is not reached for one origin, all its flows are selected.
ties	In case of equality with "nfirst" method, use "random" or "first" (see rank).
global	If TRUE flows selections is done at the matrix scale.
k	Selection threshold for nfirst, xfirst and xsumfirst methods, ratio for dominant method.
w	A vector of units weigths (sum of incoming flows, sum of outgoing flows...).

Details

If method = "dominant", select which flow (fij or fji) must be kept. If the ratio weight of destination (wj) / weight of origin (wi) is greater than k, then fij is selected and fji is not. This function can perform the second criterion of the Nystuen & Dacey's dominants flows analysis.

Value

A boolean matrix of selected flows. Use element-wise multiplication to get flows intensity.

Examples

# Import data
nav <- read.csv(system.file("csv/nav.csv", package = "flows"))
# Prepare data
mat <- prepare_mat(x = nav, i = "i", j = "j", fij = "fij")
# remove diagonal
diag(mat) <- 0

# Select the first flow from each origin
res <- select_flows(mat = mat, method = "nfirst", global = FALSE, k = 1)
rowSums(res)

# Select the 5 first flows of the matrix
res <- select_flows(mat = mat, method = "nfirst", global = TRUE, k = 5)
sum(res)

# Select the flows greater than 5000
res <- select_flows(mat = mat, method = "xfirst", k = 5000)
r <- mat * res
r[r > 0]

# Select as many flows as necessary for each origin so that their sum is at least equal to 500.
res <- select_flows(mat = mat, method = "xsumfirst", global = FALSE, k = 500)
r <- mat * res
rowSums(r)

# Select as many flows in the matrix so that their sum is at least equal to 50000.
res <- select_flows(mat = mat, method = "xsumfirst", global = TRUE, k = 50000)
r <- mat * res
sum(rowSums(r))

# Select dominant flows
m <- mat[1:5, 1:5]
ws <- colSums(m)
res <- select_flows(mat = m, method = "dominant", k = 1, w = ws)
# 2nd element has a lower weight than 3rd element (ratio > 1)
ws[3] / ws[2]
# The flow from 2nd element to 3rd element is kept
res[2, 3]
# The flow from 3rd element to 2nd element is removed
res[3, 2]

rCarto/flows documentation built on May 10, 2024, 11:38 a.m.