An interview with Chip Morningstar (and podcast hosts: Randy Farmer and Scott Moore) who created and ran the first MMOs/Virtual Worlds. This segment focuses on the emergent social phenomenon encountered the first time people used avatars with virtual currency, and artificial scarcity.
NodeXL allows users to gather vertices into named collections called “Groups”. This is handy whenever the entities in the network are made up of different types or an algorithm has divided the network into sub-regions based on how densely some vertices connect to one another. The Groups menu is found in the NodeXL>Analysis menu:
Since version v.132 of NodeXL it has been possible to Collapse a group of vertices (See: Expand and Collapse Groups of Vertices with NodeXL v.132). When a group is collapsed all of the vertices within that group are removed from the network graph and replaced with a single vertex with a size proportionate to the number of vertices in the group. A small “+” plus sign indicates that the vertex is a placeholder for a group of vertices.
If the user expands a collapsed group all of the vertices that had been hidden return to positions in the network visualization. The Groups menu has commands for creating, collapsing, and expanding groups.
NodeXL (v.166) now has the ability to automatically collapse or expand any group of vertices conditionally based on any attribute in the workbook using the Autofill Columns feature.
The NodeXL Autofill columns feature allows users to map data elements to display elements. At the bottom of this list (you may need to scroll down to see it) you will now find a new row: Group Collapsed?
There are several network metric attributes for each group that are created when the Find Groups and then the Graph Metrics command has been run on a network in NodeXL:
Selecting one of the data items in the drop down allows you to automatically decide if a group with those attributes will be presented in a collapsed or (default) expanded state. The data about each group include the number of vertices within the group, the number of connections between those vertices, the number of non-unique connections, the number of unique connections among the vertices, the number of self-connections, the number of unique connected components, the number of isolated vertices, the number of vertices in the largest component, the number of edges in the largest component, the maximum and average width of the largest component, and the density of the group.
These metrics allow for the automated processing of the graph to measure each group and apply a test to decide if a group is too dense or populous to be seen in an expanded state.
NodeXL allows collections of vertices in a network to be gathered together into a “Group”. Groups have several properties:
- groups can be selected
- vertices in selected groups can be operated on as a set
- groups can be collapsed or expanded
- network metrics can be calculated for each group
- groups can be plotted within bounded regions
NodeXL supports creating clusters or groups of vertices in several ways: by attribute or manually, by component, or algorithmically.
Group menu commands are located in the Groups Menu in the NodeXL>Analysis Menu section.
Group menu commands include:
Group by Vertex Attribute
Users can also assign vertices to groups based on any attribute in the vertex worksheet.
These attributes can be numeric, or categorical:
Groups can also be authored manually. A group is created whenever a new row is populated in the Groups worksheet. A vertex is assigned to a group when it is named with its group in the Group Vertices worksheet.
Find Connected Components:
Each component can be assigned to its own group using the NodeXL>Analysis>Groups>Find Connected Components option.
Find Clusters – Automated Group Assignment Algorithms:
NodeXL exposes three of the clustering algorithms from the Stanford Network Analysis Platform (SNAP) (http://snap.stanford.edu) library for calculating network metrics from graphs. Working with SNAP author and Stanford Computer Science Professor Jure Leskovec, the NodeXL team integrated three clustering algorithms which can be selected from Cluster>Options:
the Wakita and Tsurumi “Finding Community Structure in Mega-scale SocialNetworks” algorithm, the Girvan-Newman or Clauset-Newman-Moore algorithm. When these Group findings algorithms are run each vertex is assigned to one of a set of groups based on its decision rules. In general, these algorithms try to place collectons of densely connected vertices into separate groups or clusters.
Lists are a recent feature of Twitter which enable users to compile collections of users to follow in a single tweet stream. People can add up to 500 people to follow on a single list. People on a list may be connected to one another if one follows the other.
Some people on a list may have many connections. Some have only a few or even no connections to others on the list.
In version 161 of NodeXL you may now create maps of the connections among a list of Twitter users.
There are two options in this feature. One makes use of the List functions in Twitter. If you request the map for a single twitter list, NodeXL will build a map of the connections among all the people Twitter reports as being on the list. You can create and manage the people on a list using the Twitter list features, or select an existing Twitter list created by other users.
A second option in this feature accepts a list of up to 10,000 twitter user names pasted into the query text box. If you have a list of users and want a map of how they are connected, and the list is not already in Twitter, just paste them here and get a map.
Either way, a connection will be created for every two users if one follows the other.
Here is an example of the network map of the Twitter list of social network analysis people maintained by Valdis Krebs: valdiskrebs\network-analysts
Attractive and well designed network visualization layouts are complex to automate. Many researchers have devoted a great deal of effort to refining algorithms that assign the best set of positions to a set of nodes. In many cases a layout algorithm will work well for some types of graphs and not others. NodeXL has a few network visualization layout algorithms to choose from (Harel-Koren and Fruchterman-Reingold) and we plan to add one or two more in the coming months based on leading new approaches to automated layout.
Today, we release a new NodeXL feature in version .164 that we think will improve the results generated by other layout algorithms: Group Layout. In the Layout Options menu in the NodeXL Network Graph Pane (called “Document Actions” by Excel) you will find that the dialog box has been updated:
Selecting the new “Lay out each of the graph’s groups in its own box and sort the boxes by group size” option and checking the “Show each box’s outline” can generate an image that neatly places each group in a bounded region.
Here we see the set of connections among the people who tweeted the string “msrtf11 OR techfest” – referring to the Microsoft Research TechFest 2011 event that took place in early March in Redmond, Washington. This map clarifies the set of set of relationships among sub-groups within the graph.
Contrast this with the layout created without this feature turned on:
We still have some refinements coming that will improve this layout further (for example, the neat grid of isolated nodes takes an extra step today, we will try to make that happen automatically soon) but this is a nice step in making network graphs easier to understand. Let us know what you think!