spatsoc can be used in social network analysis to generate edge lists from GPS relocation data.

Edge lists are generated using either the edge_dist or the edge_nn function.

Note: The grouping functions and their application in social network analysis are further described in the vignette Using spatsoc in social network analysis - grouping functions.

## Generate edge lists

spatsoc provides users with one temporal (group_times) and two edge list generating functions (edge_dist, edge_nn) to generate edge lists from GPS relocations. Users can consider edges defined by either the spatial proximity between individuals (with edge_dist), by nearest neighbour (with edge_nn) or by nearest neighbour with a maximum distance (with edge_nn). The edge lists can be used directly by the animal social network package asnipe to generate networks.

### 1. Load packages and prepare data

spatsoc expects a data.table for all DT arguments and date time columns to be formatted POSIXct.

## Load packages
library(spatsoc)
library(data.table)

## Read data as a data.table
DT <- fread(system.file("extdata", "DT.csv", package = "spatsoc"))

## Cast datetime column to POSIXct
DT[, datetime := as.POSIXct(datetime)]

Next, we will group relocations temporally with group_times and generate edges lists with one of edge_dist, edge_dist. Note: these are mutually exclusive, only select one edge list generating function at a time.

### 2. a) edge_dist

Distance based edge lists where relocations in each timegroup are considered edges if they are within the spatial distance defined by the user with the threshold argument. Depending on species and study system, relevant temporal and spatial distance thresholds are used. In this case, relocations within 5 minutes and 50 meters are considered edges.

This is the non-chain rule implementation similar to group_pts. Edges are defined by the distance threshold and NAs are returned for individuals within each timegroup if they are not within the threshold distance of any other individual (if fillNA is TRUE).

Optionally, edge_dist can return the distances between individuals (less than the threshold) in a column named ‘distance’ with argument returnDist = TRUE.

# Temporal groups
group_times(DT, datetime = 'datetime', threshold = '5 minutes')
#>        ID        X       Y            datetime population minutes timegroup
#>     1:  A 715851.4 5505340 2016-11-01 00:00:54          1       0         1
#>     2:  A 715822.8 5505289 2016-11-01 02:01:22          1       0         2
#>     3:  A 715872.9 5505252 2016-11-01 04:01:24          1       0         3
#>     4:  A 715820.5 5505231 2016-11-01 06:01:05          1       0         4
#>     5:  A 715830.6 5505227 2016-11-01 08:01:11          1       0         5
#>    ---
#> 14293:  J 700616.5 5509069 2017-02-28 14:00:54          1       0      1393
#> 14294:  J 700622.6 5509065 2017-02-28 16:00:11          1       0      1394
#> 14295:  J 700657.5 5509277 2017-02-28 18:00:55          1       0      1449
#> 14296:  J 700610.3 5509269 2017-02-28 20:00:48          1       0      1395
#> 14297:  J 700744.0 5508782 2017-02-28 22:00:39          1       0      1396

# Edge list generation
edges <- edge_dist(
DT,
threshold = 100,
id = 'ID',
coords = c('X', 'Y'),
timegroup = 'timegroup',
returnDist = TRUE,
fillNA = TRUE
)

### 2. b) edge_nn

Nearest neighbour based edge lists where each individual is connected to their nearest neighbour. edge_nn can be used to generate edge lists defined either by nearest neighbour or nearest neighbour with a maximum distance. As with grouping functions and edge_dist, temporal and spatial threshold depend on species and study system.

NAs are returned for nearest neighbour for an individual was alone in a timegroup (and/or splitBy) or if the distance between an individual and its nearest neighbour is greater than the threshold.

Optionally, edge_nn can return the distances between individuals (less than the threshold) in a column named ‘distance’ with argument returnDist = TRUE.

# Temporal groups
group_times(DT, datetime = 'datetime', threshold = '5 minutes')

# Edge list generation
edges <- edge_nn(
DT,
id = 'ID',
coords = c('X', 'Y'),
timegroup = 'timegroup'
)

# Edge list generation using maximum distance threshold
edges <- edge_nn(
DT,
id = 'ID',
coords = c('X', 'Y'),
timegroup = 'timegroup',
threshold = 100
)

# Edge list generation using maximum distance threshold, returning distances
edges <- edge_nn(
DT,
id = 'ID',
coords = c('X', 'Y'),
timegroup = 'timegroup',
threshold = 100,
returnDist = TRUE
)

### 3. dyad_id

The function dyad_id can be used to generate a unique, undirected dyad identifier for edge lists.

# In this case, using the edges generated in 2. a) edge_dist
dyad_id(edges, id1 = 'ID1', id2 = 'ID2')
#>        timegroup ID1  ID2  distance dyadID
#>     1:         1   A <NA>        NA   <NA>
#>     2:         1   B    G  5.782904    B-G
#>     3:         1   C <NA>        NA   <NA>
#>     4:         1   D <NA>        NA   <NA>
#>     5:         1   E    H 65.061671    E-H
#>    ---
#> 22942:      1457   G <NA>        NA   <NA>
#> 22943:      1458   H <NA>        NA   <NA>
#> 22944:      1459   I <NA>        NA   <NA>
#> 22945:      1460   J <NA>        NA   <NA>
#> 22946:      1461   J <NA>        NA   <NA>

Once we have generated dyad ids, we can measure consecutive relocations, start and end relocation, etc. Note: since the edges are duplicated A-B and B-A, you will need to use the unique timegroup*dyadID or divide counts by 2.

# Get the unique dyads by timegroup

# Set the order of the rows

## Count number of timegroups dyads are observed together

## Count consecutive relocations together
# Shift the timegroup within dyadIDs

# Difference between consecutive timegroups for each dyadID
# where difftimegrp == 1, the dyads remained together in consecutive timegroups
dyads[, difftimegrp := timegroup - shifttimegrp]

# Run id of diff timegroups

# N consecutive observations of dyadIDs
dyads[, runCount := fifelse(difftimegrp == 1, .N, NA_integer_), by = .(runid, dyadID)]

## Start and end of consecutive relocations for each dyad
# Dont consider where runs aren't more than one relocation
dyads[runCount > 1, start := fifelse(timegroup == min(timegroup), TRUE, NA), by = .(runid, dyadID)]

dyads[runCount > 1, end := fifelse(timegroup == max(timegroup), TRUE, NA), by = .(runid, dyadID)]

## Example output
.(timegroup, nObs, shifttimegrp, difftimegrp, runid, runCount, start, end)]
#>     timegroup nObs shifttimegrp difftimegrp runid runCount start  end
#>  1:      1340   29           NA          NA     1       NA    NA   NA
#>  2:      1341   29         1340           1     2        3  TRUE   NA
#>  3:      1342   29         1341           1     2        3    NA   NA
#>  4:      1343   29         1342           1     2        3    NA TRUE
#>  5:      1346   29         1343           3     3       NA    NA   NA
#>  6:      1347   29         1346           1     4        3  TRUE   NA
#>  7:      1348   29         1347           1     4        3    NA   NA
#>  8:      1349   29         1348           1     4        3    NA TRUE
#>  9:      1351   29         1349           2     5       NA    NA   NA
#> 10:      1356   29         1351           5     6       NA    NA   NA
#> 11:      1357   29         1356           1     7        2  TRUE   NA
#> 12:      1358   29         1357           1     7        2    NA TRUE
#> 13:      1360   29         1358           2     8       NA    NA   NA
#> 14:      1361   29         1360           1     9        1    NA   NA
#> 15:      1364   29         1361           3    10       NA    NA   NA
#> 16:      1383   29         1364          19    11       NA    NA   NA
#> 17:      1384   29         1383           1    12        7  TRUE   NA
#> 18:      1385   29         1384           1    12        7    NA   NA
#> 19:      1386   29         1385           1    12        7    NA   NA
#> 20:      1387   29         1386           1    12        7    NA   NA
#> 21:      1388   29         1387           1    12        7    NA   NA
#> 22:      1389   29         1388           1    12        7    NA   NA
#> 23:      1390   29         1389           1    12        7    NA TRUE
#> 24:      1392   29         1390           2    13       NA    NA   NA
#> 25:      1393   29         1392           1    14        3  TRUE   NA
#> 26:      1394   29         1393           1    14        3    NA   NA
#> 27:      1395   29         1394           1    14        3    NA TRUE
#> 28:      1445   29         1395          50    15       NA    NA   NA
#> 29:      1446   29         1445           1    16        1    NA   NA
#>     timegroup nObs shifttimegrp difftimegrp runid runCount start  end