define_retra {ecoregime}

Define representative trajectories from trajectory features

Description

Generate an object of class RETRA from a data frame containing trajectory states to define representative trajectories in Ecological Dynamic Regimes (EDR).

Usage

define_retra(data, d = NULL, trajectories = NULL, states = NULL, retra = NULL)

Arguments

data

A data frame of four columns indicating identifiers for the new representative trajectories, the individual trajectories or sites to which the states belong, the order of the states in the individual trajectories, and the identifier of the representative trajectory to which the states belong (only if !is.null(retra)). Alternatively, 'data' can be a vector or a list of character vectors including the sequence of segments forming the new representative trajectory. See Details for further clarifications to define data.

d

Either a symmetric matrix or an object of class dist containing the dissimilarities between each pair of states of all trajectories in the EDR. If NULL (default), the length (Length) of the new representative trajectories and the distances between states of different trajectories or sites (Link_distance) are not calculated.

trajectories

Only needed if !is.null(d). Vector indicating the trajectory or site to which each state in d belongs.

states

Only needed if !is.null(d). Vector of integers indicating the order of the states in d for each trajectory.

retra

Object of class RETRA returned from retra_edr(). If NULL (default), minSegs and Seg_density are not provided for the new representative trajectories.

Details

Each representative trajectory returned by the function retra_edr() corresponds to the longest sequence of representative segments that can be linked according to the criteria defined in the RETRA-EDR algorithm (Sánchez-Pinillos et al., 2023). One could be interested in splitting the obtained trajectories, considering only a fraction of the returned trajectories, or defining representative trajectories following different criteria than those in RETRA-EDR. The function define_retra() allows generating an object of class RETRA that can be used in other functions of ecoregime (e.g., plot()).

For that, it is necessary to provide information about the set of segments or trajectory states that form the new representative trajectory through the argument data:

• data can be defined as a data frame with as many rows as the number of states in all representative trajectories and the following columns:

  RT

  A string indicating the identifier of the new representative trajectories. Each identifier needs to appear as many times as the number of states forming each representative trajectory.

  RT_traj

  A vector indicating the individual trajectories in the EDR to which each state of the new representative trajectory belongs.

  RT_states

  A vector of integers indicating the identifier of the states forming the new representative trajectories. Each integer must refer to the order of the states in the individual trajectories of the EDR to which they belong.

  RT_retra

  Only if the new trajectories are defined from representative trajectories returned by retra_edr() (when !is.null(retra)). A vector of strings indicating the representative trajectory in retra to which each state belongs.

• Alternatively, data can be defined as either a vector (if there is one representative trajectory) or a list of character vectors (with as many elements as the number of representative trajectories desired) containing the sequence of segments of the representative trajectories. In any case, each segment needs to be specified in the form traj[st1-st2], where traj is the identifier of the original trajectory to which the segment belongs and st1 and st2 are identifiers of the initial and final states defining the segment. If only one state of an individual trajectory is considered to form the representative trajectory, the corresponding segment needs to be defined as traj[st-st].

Value

An object of class RETRA, which is a list of length equal to the number of representative trajectories defined. For each trajectory, the following information is returned:

minSegs

Value of the minSegs parameter used in retra_edr(). If retra is NULL, minSegs = NA.

Segments

Vector of strings including the sequence of segments forming the representative trajectory. Each segment is identified by a string of the form traj[st1-st2], where traj is the identifier of the original trajectory to which the segment belongs and st1 and st2 are identifiers of the initial and final states defining the segment. The same format traj[st1-st2] is maintained when only one state of an individual trajectory is considered (st1 = st2). traj, st1, and st2 are recycled from data.

Size

Integer indicating the number of states forming the representative trajectory.

Length

Numeric value indicating the length of the representative trajectory, calculated as the sum of the dissimilarities in d between every pair of consecutive states. If d is NULL, Length = NA.

Link_distance

Data frame of two columns indicating artificial links between two segments (Link) and the dissimilarity between the connected states (Distance). When two representative segments are linked by a common state or by two consecutive states of the same trajectory, the link distance is zero or equal to the length of a real segment, respectively. In both cases, the link is not considered in the returned data frame. If d is NULL, Link_distance = NA.

Seg_density

Data frame of two columns and one row for each representative segment. Density contains the number of segments in the EDR that is represented by each segment of the representative trajectory. kdTree_depth contains the depth of the k-d tree for each leaf represented by the corresponding segment. That is, the number of partitions of the ordination space until finding a region with minSegs segments or less. If retra is NULL, Seg_density = NA.

Author(s)

Martina Sánchez-Pinillos

See Also

retra_edr() for identifying representative trajectories in EDRs through RETRA-EDR.

summary() for summarizing the characteristics of the representative trajectories.

plot() for plotting representative trajectories in an ordination space representing the state space of the EDR.

Examples

# Example 1 -----------------------------------------------------------------
# Define representative trajectories from the outputs of retra_edr().

# Identify representative trajectories using retra_edr()
d <- EDR_data$EDR1$state_dissim
trajectories <- EDR_data$EDR1$abundance$traj
states <- EDR_data$EDR1$abundance$state
old_retra <- retra_edr(d = d, trajectories = trajectories, states = states,
                       minSegs = 5)

# retra_edr() returns three representative trajectories
old_retra

# Keep the last five segments of trajectories "T2" and "T3"
selected_segs <- old_retra$T2$Segments[4:length(old_retra$T2$Segments)]

# Identify the individual trajectories for each state...
selected_segs
selected_traj <- rep(c(15, 4, 4, 1, 14), each = 2)

# ...and the states (in the same order as the representative trajectory).
selected_states <- c(1, 2, 2, 3, 3, 4, 1, 2, 2, 3)

# Generate the data frame with the format indicated in the documentation
df <- data.frame(RT = rep("A", length(selected_states)),
                 RT_traj = selected_traj,
                 RT_states = as.integer(selected_states),
                 RT_retra = rep("T2", length(selected_states)))

# Remove duplicates (trajectory 4, state 3)
df <- unique(df)

# Generate a RETRA object using define_retra()
new_retra <- define_retra(data = df,
                          d = d,
                          trajectories = trajectories,
                          states = states,
                          retra = old_retra)

# Example 2 -----------------------------------------------------------------
# Define representative trajectories from sequences of segments

# Select all segments in T1, split T2 into two new trajectories, and include
# a trajectory composed of states belonging to trajectories "5", "6", and "7"
data <- list(old_retra$T1$Segments,
             old_retra$T2$Segments[1:3],
             old_retra$T2$Segments[4:8],
             c("5[1-2]", "5[2-3]", "7[4-4]", "6[4-5]"))

# Generate a RETRA object using define_retra()
new_retra <- define_retra(data = data,
                          d = d,
                          trajectories = trajectories,
                          states = states,
                          retra = old_retra)

# Example 3 -----------------------------------------------------------------
# Define two representative trajectories from individual trajectories in EDR1.

# Define trajectory "A" from states in trajectories 3 and 4
data_A <- data.frame(RT = rep("A", 4),
                     RT_traj = c(3, 3, 4, 4),
                     RT_states = c(1:2, 4:5))

# Define trajectory "B" from states in trajectories 5, 6, and 7
data_B <- data.frame(RT = rep("B", 5),
                     RT_traj = c(5, 5, 7, 6, 6),
                     RT_states = c(1, 2, 4, 4, 5))

# Compile data for both trajectories in a data frame
df <- rbind(data_A, data_B)
df$RT_states <- as.integer(df$RT_states)

# Generate a RETRA object using define_retra()
new_retra <- define_retra(data = df, d = EDR_data$EDR1$state_dissim,
                          trajectories = EDR_data$EDR1$abundance$traj,
                          states = EDR_data$EDR1$abundance$state)