Dash Callbacks for Cytoscape
Dash callbacks allow you to update your
Cytoscape graph via other components like dropdowns, buttons, and sliders.
If you have used Cytoscape.js before, you have probably used event handlers
to interactively update your graph; with Dash Cytoscape, we will instead
use callbacks.
Changing Layouts
Consider the graph containing North American cities from the layout
chapter. We have shown in that chapter how to display the same graph in
multiple layouts. But what if we want to introduce the option for the
user to interactively update the layouts?
Recall the declaration of the graph:
using Dash, DashCytoscape
app = dash()
nodes = [
Dict(
"data" => Dict("id" => short, "label" => label),
"position" => Dict("x" => 20*lat, "y" => -20*long)
)
for (short, label, long, lat) in (
("la", "Los Angeles", 34.03, -118.25),
("nyc", "New York", 40.71, -74),
("to", "Toronto", 43.65, -79.38),
("mtl", "Montreal", 45.50, -73.57),
("van", "Vancouver", 49.28, -123.12),
("chi", "Chicago", 41.88, -87.63),
("bos", "Boston", 42.36, -71.06),
("hou", "Houston", 29.76, -95.37)
)
]
edges = [
Dict("data" => Dict("source" => source, "target" => target))
for (source, target) in (
("van", "la"),
("la", "chi"),
("hou", "chi"),
("to", "mtl"),
("mtl", "bos"),
("nyc", "bos"),
("to", "hou"),
("to", "nyc"),
("la", "nyc"),
("nyc", "bos")
)
]
elements = vcat(nodes, edges)
app.layout = html_div([
cyto_cytoscape(
id="cytoscape-callbacks-1",
elements=elements,
style=Dict("width" => "100%", "height" => "400px"),
layout=Dict(
"name" => "grid"
)
)
])
run_server(app, "0.0.0.0", debug=true)
What we want to modify is the argument to layout. To do so, we could use
a dash_core_components.Dropdown with the name of the layouts as options.
We could set the default value to ‘grid’, and force it to be unclearable
(since we do not want to pass a dictionary with null value to Cytoscape).
using Dash, DashCytoscape
app = dash()
app.layout = dcc_dropdown(
id="dropdown-callbacks-1",
value="grid",
clearable=false,
options=[
Dict("label" => uppercase(name), "value" => name)
for name in ["grid", "random", "circle", "cose", "concentric"]
]
)
run_server(app, "0.0.0.0", debug=true)
The construction of the callback becomes extremely easy. We simply create
a function as such:
callback!(app,
Output("cytoscape-callbacks-1", "layout"),
Input("dropdown-callbacks-1", "value")
) do layout
return Dict(
"name" => layout
)
end
In fact, it is even possible to animate the layouts after an update!
Simply enable animate:
callback!(app,
Output("cytoscape-callbacks-1", "layout"),
Input("dropdown-callbacks-1", "value")
) do layout
return Dict(
"name" => layout,
"animate" => true
)
end
Piecing everything together, we get:
using Dash, DashCytoscape
app = dash()
nodes = [
Dict(
"data" => Dict("id" => short, "label" => label),
"position" => Dict("x" => 20*lat, "y" => -20*long)
)
for (short, label, long, lat) in (
("la", "Los Angeles", 34.03, -118.25),
("nyc", "New York", 40.71, -74),
("to", "Toronto", 43.65, -79.38),
("mtl", "Montreal", 45.50, -73.57),
("van", "Vancouver", 49.28, -123.12),
("chi", "Chicago", 41.88, -87.63),
("bos", "Boston", 42.36, -71.06),
("hou", "Houston", 29.76, -95.37)
)
]
edges = [
Dict("data" => Dict("source" => source, "target" => target))
for (source, target) in (
("van", "la"),
("la", "chi"),
("hou", "chi"),
("to", "mtl"),
("mtl", "bos"),
("nyc", "bos"),
("to", "hou"),
("to", "nyc"),
("la", "nyc"),
("nyc", "bos")
)
]
elements = vcat(nodes, edges)
app.layout = html_div([
dcc_dropdown(
id="dropdown-update-layout",
value="grid",
clearable=false,
options=[
Dict("label" => uppercase(name), "value" => name)
for name in ["grid", "random", "circle", "cose", "concentric"]
]
),
cyto_cytoscape(
id="cytoscape-update-layout",
elements=elements,
style=Dict("width" => "100%", "height" => "450px"),
layout=Dict(
"name" => "grid"
)
)
])
callback!(app,
Output("cytoscape-update-layout", "layout"),
Input("dropdown-update-layout", "value")
) do layout
return Dict(
"name" => layout,
"animate" => true
)
end
run_server(app, "0.0.0.0", debug=true)
Notice we did not include an animation for
preset. As discussed in the layout chapter, you
will need to specify the position of the nodes inside of thelayoutdictionary.
Interactively update styles
Updating the stylesheet using Dash components is similar to updating
layouts, although it can get more complex. Indeed, you can choose to create
a default stylesheet, and append new styles to that stylesheet every time
a designated callback is fired. Let’s take the following stylesheet:
default_stylesheet = [
Dict(
"selector" => "node",
"style" => Dict(
"background-color" => "#BFD7B5",
"label" => "data(label)"
)
),
Dict(
"selector" => "edge",
"style" => Dict(
"line-color" => "#A3C4BC"
)
)
]
This is generally declared at the beginning of your script, before layout
declaration (therefore it is shared across sessions). The city graph will
look something like this:
using Dash, DashCytoscape
app = dash()
nodes = [
Dict(
"data" => Dict("id" => short, "label" => label),
"position" => Dict("x" => 20*lat, "y" => -20*long)
)
for (short, label, long, lat) in (
("la", "Los Angeles", 34.03, -118.25),
("nyc", "New York", 40.71, -74),
("to", "Toronto", 43.65, -79.38),
("mtl", "Montreal", 45.50, -73.57),
("van", "Vancouver", 49.28, -123.12),
("chi", "Chicago", 41.88, -87.63),
("bos", "Boston", 42.36, -71.06),
("hou", "Houston", 29.76, -95.37)
)
]
edges = [
Dict("data" => Dict("source" => source, "target" => target))
for (source, target) in (
("van", "la"),
("la", "chi"),
("hou", "chi"),
("to", "mtl"),
("mtl", "bos"),
("nyc", "bos"),
("to", "hou"),
("to", "nyc"),
("la", "nyc"),
("nyc", "bos")
)
]
elements = vcat(nodes, edges)
default_stylesheet = [
Dict(
"selector" => "node",
"style" => Dict(
"background-color" => "#BFD7B5",
"label" => "data(label)"
)
),
Dict(
"selector" => "edge",
"style" => Dict(
"line-color" => "#A3C4BC"
)
)
]
app.layout = cyto_cytoscape(
id="cytoscape-callbacks-2",
elements=elements,
stylesheet=default_stylesheet,
style=Dict("width" => "100%", "height" => "400px"),
layout=Dict(
"name" => "circle"
)
)
run_server(app, "0.0.0.0", debug=true)
We might want to use text fields to input the color we want to add:
using Dash
app = dash()
app.layout = html_div([
html_div(style=Dict("width" => "50%", "display" => "inline"), children=[
"Edge Color: ",
dcc_input(id="input-line-color", type="text")
]),
html_div(style=Dict("width" => "50%", "display" => "inline"), children=[
"Node Color: ",
dcc_input(id="input-bg-color", type="text")
])
])
run_server(app, "0.0.0.0", debug=true)
All we need now is to assign a callback that will add new styles to the
default stylesheet in order to change the default color:
callback!(app,
Output("cytoscape-callbacks-2", "stylesheet"),
Input("input-line-color", "value"),
Input("input-bg-color", "value")
) do line_color, bg_color
if line_color isa Nothing
line_color = ""
end
if bg_color isa Nothing
bg_color = ""
end
new_styles = [
Dict(
"selector" => "node",
"style" => Dict(
"background-color" => bg_color
)
),
Dict(
"selector" => "edge",
"style" => Dict(
"line-color" => line_color
)
)
]
return vcat(default_stylesheet, new_styles)
end
Notice that we are setting the line and background color to an empty
string when they are set to nothing; this is to avoid feeding nothing to the dictionary, since it is not accepted by Cytoscape.
However, passing any string value to the dictionary is accepted, even when
the string value is not recognized. Therefore, the callback is fired every
time you type a new character, but the changes are only applied when
Cytoscape recognizes the input, which in this case could be the name of
a color, the hex code, or the rgb function.
Below, we show how the entire app is constructed:
using Dash, DashCytoscape
app = dash()
nodes = [
Dict(
"data" => Dict("id" => short, "label" => label),
"position" => Dict("x" => 20*lat, "y" => -20*long)
)
for (short, label, long, lat) in (
("la", "Los Angeles", 34.03, -118.25),
("nyc", "New York", 40.71, -74),
("to", "Toronto", 43.65, -79.38),
("mtl", "Montreal", 45.50, -73.57),
("van", "Vancouver", 49.28, -123.12),
("chi", "Chicago", 41.88, -87.63),
("bos", "Boston", 42.36, -71.06),
("hou", "Houston", 29.76, -95.37)
)
]
edges = [
Dict("data" => Dict("source" => source, "target" => target))
for (source, target) in (
("van", "la"),
("la", "chi"),
("hou", "chi"),
("to", "mtl"),
("mtl", "bos"),
("nyc", "bos"),
("to", "hou"),
("to", "nyc"),
("la", "nyc"),
("nyc", "bos")
)
]
elements = vcat(nodes, edges)
default_stylesheet = [
Dict(
"selector" => "node",
"style" => Dict(
"background-color" => "#BFD7B5",
"label" => "data(label)"
)
),
Dict(
"selector" => "edge",
"style" => Dict(
"line-color" => "#A3C4BC"
)
)
]
app.layout = html_div([
html_div([
html_div(style=Dict("width" => "50%", "display" => "inline"), children=[
"Edge Color: ",
dcc_input(id="input-line-color", type="text")
]),
html_div(style=Dict("width" => "50%", "display" => "inline"), children=[
"Node Color: ",
dcc_input(id="input-bg-color", type="text")
])
]),
cyto_cytoscape(
id="cytoscape-stylesheet-callbacks",
elements=elements,
stylesheet=default_stylesheet,
style=Dict("width" => "100%", "height" => "400px"),
layout=Dict(
"name" => "circle"
)
)
])
callback!(app,
Output("cytoscape-stylesheet-callbacks", "stylesheet"),
Input("input-line-color", "value"),
Input("input-bg-color", "value")
) do line_color, bg_color
if line_color isa Nothing
line_color = ""
end
if bg_color isa Nothing
bg_color = ""
end
new_styles = [
Dict(
"selector" => "node",
"style" => Dict(
"background-color" => bg_color
)
),
Dict(
"selector" => "edge",
"style" => Dict(
"line-color" => line_color
)
)
]
return vcat(default_stylesheet, new_styles)
end
run_server(app, "0.0.0.0", debug=true)
In this example, we are not appending the new styles
directly to the default style, but instead concatenating
default_stylesheet with new_styles. This is because any modification
to default_stylesheet will be permanent, which is not a good thing if you
are hosting your app for many users (since default_stylesheet is shared
across all user sessions).
Adding and removing elements
One useful aspect of callbacks is the ability to add and remove elements.
By using elements as a state of your callback, you can decide to manipulate
it in order to add elements whenever another Dash component is updated.
Let’s take as an example a simple app where you can add and remove nodes
by clicking two html buttons (with the same graph as above):
using Dash
app = dash()
app.layout = html_div([
html_button("Add Node", id="btn-add-node-example", n_clicks_timestamp=0),
html_button("Remove Node", id="btn-remove-node-example", n_clicks_timestamp=0)
])
run_server(app, "0.0.0.0", debug=true)
The following callback would be needed:
callback!(app,
Output("cytoscape-callbacks-2", "elements"),
Input("btn-add-node-example", "n_clicks_timestamp"),
Input("btn-remove-node-example", "n_clicks_timestamp"),
State("cytoscape-callbacks-2", "elements")
) do btn_add, btn_remove, elements
# If the add button was clicked most recently
if Int(btn_add) > Int(btn_remove)
next_node_idx = count(isdefined.(elements,Symbol("position")))
# As long as we have not reached the max number of nodes, we add them
# to the cytoscape elements
if next_node_idx < length(nodes)
new_nodes = nodes[1:next_node_idx+1]
node_ids = map(x->x["data"]["id"], new_nodes)
locs = map(x->(
(x["data"]["target"] ∈ node_ids ) &&
(x["data"]["source"] ∈ node_ids)
),edges)
return vcat(edges[locs], new_nodes)
end
# If the remove button was clicked most recently
elseif Int(btn_remove) > Int(btn_add)
if length(elements) > length(edges)
return elements[1:end-1]
end
end
# # Neither have been clicked yet (or fallback condition)
return elements
end
The first conditional if int(btn_add) > int(btn_remove) verifies whether
the add button was just clicked. If it wasn’t, then the remove button is
verified with elif int(btn_remove) > int(btn_add). If neither were clicked,
then we return the default elements.
The second part of the conditional verifies whether there are nodes to add or
remove. If neither conditions are met, we simply return the current elements.
It’s important to mutate the elements object by passing it into the
callbacks as State (which is what we are doing here) rather than making
it a global variable. In general, global variables should be avoided
as they won’t work when multiple users are viewing the app or when the app
is deployed with multiple gunicorn workers.
You can find the complete app below:
using Dash, DashCytoscape
app = dash()
nodes = [
Dict(
"data" => Dict("id" => short, "label" => label),
"position" => Dict("x" => 20*lat, "y" => -20*long)
)
for (short, label, long, lat) in (
("la", "Los Angeles", 34.03, -118.25),
("nyc", "New York", 40.71, -74),
("to", "Toronto", 43.65, -79.38),
("mtl", "Montreal", 45.50, -73.57),
("van", "Vancouver", 49.28, -123.12),
("chi", "Chicago", 41.88, -87.63),
("bos", "Boston", 42.36, -71.06),
("hou", "Houston", 29.76, -95.37)
)
]
edges = [
Dict("data" => Dict("source" => source, "target" => target))
for (source, target) in (
("van", "la"),
("la", "chi"),
("to", "mtl"),
("mtl", "bos"),
("nyc", "bos"),
("to", "hou"),
("to", "nyc"),
("la", "nyc"),
("nyc", "bos")
)
]
default_stylesheet = [
Dict(
"selector" => "node",
"style" => Dict(
"background-color" => "#BFD7B5",
"label" => "data(label)"
)
),
Dict(
"selector" => "edge",
"style" => Dict(
"line-color" => "#A3C4BC"
)
)
]
app.layout = html_div([
html_div([
html_button("Add Node", id="btn-add-node", n_clicks_timestamp=0),
html_button("Remove Node", id="btn-remove-node", n_clicks_timestamp=0)
]),
cyto_cytoscape(
id="cytoscape-elements-callbacks",
layout=Dict("name" => "circle"),
stylesheet=default_stylesheet,
style=Dict("width" => "100%", "height" => "450px"),
elements=vcat(edges, nodes)
)
])
callback!(app,
Output("cytoscape-elements-callbacks", "elements"),
Input("btn-add-node", "n_clicks_timestamp"),
Input("btn-remove-node", "n_clicks_timestamp"),
State("cytoscape-elements-callbacks", "elements")
) do btn_add, btn_remove, elements
# If the add button was clicked most recently
if Int(btn_add) > Int(btn_remove)
next_node_idx = count(isdefined.(elements,Symbol("position")))
# As long as we have not reached the max number of nodes, we add them
# to the cytoscape elements
if next_node_idx < length(nodes)
new_nodes = nodes[1:next_node_idx+1]
node_ids = map(x->x["data"]["id"], new_nodes)
locs = map(x->(
(x["data"]["target"] ∈ node_ids ) &&
(x["data"]["source"] ∈ node_ids)
),edges)
return vcat(edges[locs], new_nodes)
end
# If the remove button was clicked most recently
elseif Int(btn_remove) > Int(btn_add)
if length(elements) > length(edges)
return elements[1:end-1]
end
end
# # Neither have been clicked yet (or fallback condition)
return elements
end
run_server(app, "0.0.0.0", debug=true)