DiagrammeR (version 0.9.0)

mutate_edge_attrs: Mutate a set of edge attribute values

Description

Within a graph's internal edge data frame (edf), mutate numeric edge attribute values using one or more expressions. Optionally, one can specify a different edge attribute name and create a new edge attribute while retaining the original edge attribute and its values.

Usage

mutate_edge_attrs(graph, edge_attr_from, expressions, edge_attr_to = NULL)

Arguments

graph

a graph object of class dgr_graph.

edge_attr_from

the name of the edge attribute column from which values will be mutated. An NA value can be provided here if edge attribute names are used in expressions statements. Note that if NA is used, a value must be provided for edge_attr_to.

expressions

one or more expressions for mutation of all edge attribute values specified by edge_attr_from. To reference the edge attribute given in edge_attr_from, use the ~ character. Otherwise, all edge attributes can be referenced by using the names of those edge attributes directly in the expressions. Expressions are evaluated in the order provided.

edge_attr_to

an optionally supplied name of a new edge attribute to which the mutated values will be applied. This will retain the original edge attribute and its values. If NA is used with edge_attr_from, a value must be provided here (since mutated values must be placed somewhere).

Value

a graph object of class dgr_graph.

Examples

# NOT RUN {
# Create a graph with 3 edges
graph <-
  create_graph() %>%
  add_path(4) %>%
  set_edge_attrs(
    "width", c(3.4, 2.3, 7.2))

# Get the graph's internal edf to show which
# edge attributes are available
get_edge_df(graph)
#>   id from to  rel width
#> 1  1    1  2 <NA>   3.4
#> 2  2    2  3 <NA>   2.3
#> 3  3    3  4 <NA>   7.2

# Mutate the `width` edge attribute, dividing
# each value by 2
graph <-
  graph %>%
  mutate_edge_attrs("width", "~ / 2")

# Get the graph's internal edf to show that the
# edge attribute `width` had its values changed
get_edge_df(graph)
#>   id from to  rel width
#> 1  1    1  2 <NA>  1.70
#> 2  2    2  3 <NA>  1.15
#> 3  3    3  4 <NA>  3.60

# Create a new edge attribute, called `length`,
# that is the log of values in `width` plus 2
# (and round all values to 2 decimal places)
graph <-
  graph %>%
  mutate_edge_attrs(
    "width", "round(log(~) + 2, 2)", "length")

# Get the graph's internal edf to show that
# the edge attribute values had been mutated
# and used as the new edge attribute `length`
get_edge_df(graph)
#>   id from to  rel width length
#> 1  1    1  2 <NA>  1.70   2.53
#> 2  2    2  3 <NA>  1.15   2.14
#> 3  3    3  4 <NA>  3.60   3.28

# Create a new edge attribute called `area`,
# which is the product of the `width` and
# `length` attributes; note that we can provide
# NA to `edge_attr_from` since we are naming
# at least one of the edge attributes in the
# `expressions` vector (and providing a new
# edge attribute name: `area`)
graph <-
  graph %>%
  mutate_edge_attrs(
    NA, "width * length", "area")

# Get the graph's internal edf to show that
# the edge attribute values had been multiplied
# together, creating a new edge attribute `area`
get_edge_df(graph)
#>   id from to  rel width length   area
#> 1  1    1  2 <NA>  1.70   2.53  4.301
#> 2  2    2  3 <NA>  1.15   2.14  2.461
#> 3  3    3  4 <NA>  3.60   3.28 11.808
# }