`nw2set`

Declare data to be two-mode network data

Syntax

Declare data to be two-mode network data
nw2set varlist [, options ]
nw2set
,
mat(matamatrix)
[ options ]


`edgelist`	declare data in edgelist format
`name`(newnetname)	name of the new network; default = network
`labs`(lab1 lab2…)	new node labels that are used for the network
`rownames(varname)`	names of nodes on level 2
`xvars`	generate Stata variables for the network
`vars(namelist)`	Stata variable names to store the network as (one per node, level 1 then level 2); default = auto-generated
`clear`	drop all existing networks (but not the Stata dataset) before declaring this one
`nwclear`	same as `clear`

Description

This command declares data to be two-mode network data. A two-mode network consists of two sets of units (e. g. people and events) and relations connect the two sets, e. g. participation of people in social events. Some examples are:

Membership in institutions - people, institutions, is a member, e.g. directors and commissioners on the boards of corporations.
Voting for suggestions - polititians, suggestions, votes for.
Citation network, where first set consists of authors, the second set consists of articles/papers, connection is a relation author cites a paper.
Co-autorship networks - authors, papers, is a (co)author.

A corresponding graph is called bipartite graph – lines connect only vertices from one to vertices from another set – inside sets there are no connections.

Setting two-mode networks is very similar to setting normal networks with nwset. With M nodes on level 1 and N nodes on level 2, the command internally generates a (M+N) x (M+N) matrix, which stores the network data. Furthermore, it generates a variable _mode, which has the value 1 for nodes on level 1 (e.g. persons: Peter, Tim, Thomas, Michael, Mathilde) and value 2 for nodes on level 2 (e.g institutions: LiU, UCD, Oxford, ETH).

When a network is set as two-mode, this meta-information is stored with the network. Other nwcommands automatically recognize that the network is two-mode and deal with it accordingly (e.g. nwplot).

There are three ways to explicitly declare data to be two-mode network data:

ul:1. Declare adjacency matrix from variables

Declare the variables in varlist to represent the adjacency matrix of the two-mode network. In this case a varlist (var_1, var_2,…, var_z) needs to be given. Each variable stands for a node on level 1 (e.g. organisations). Each row in the dataset stands for a node on level 2 (e.g. persons).

In this dummy example we create 5 observations and 3 new variables v1-v3. After that we set a two-mode network from this data. This creates an empty network with 5 nodes on level 1 and 3 nodes on level 2.

. nwclear
. set obs 5
. forvalues i = 1/3{
gen v = 0
}
. nw2set v*

By default, the nodes on level 1 are named after the variables v1, v2 and v3. If option rownames(varname) is specified, the nodes on level 2 are named afther the values found in variable varname.

ul:2. Declare edgelist from variables

In this case, the command interprets the variables varlist as egdelist (see nw2fromedge).

An edgelist or arclist is a set of two (or three in the case of a valued network) variables representing relations. Nodes are identified by entries in the cells. For example, imagine the following kind of data:

hline 18c -
c fromid toid c
hline 18c -
1. c Peter LiU c
1. c Andreas UCD c
1. c Thomas UCD c
hline 18c -

We can declare this data as a two-mode network like this:

. nw2set fromid toid, egdelist

This commands generates a network with 5 nodes in total; 3 nodes on level 1 (Peter, Andreas, Thomas) and 2 nodes on level 2 (LiU, UCD).

ul:2. Declare adjacency matrix from Mata matrix

Set a network from a M x N Mata matrix that holds the adjacency matrix of the new network with N nodes on level 1 and M nodes on level 2. The option mat() is specified with the name of an existing Mata matrix.

For example, this generates a Mata matrix and sets a two-mode network with 6 nodes (4 nodes in level 1 and 2 nodes on level 2):

. nwclear
. mata: net = (0,1\1,0\1,1\1,1)
. nw2set, mat(net) name(network)

Remarks

By default, two-mode networks are undirected.

By default, network generators (including nw2set itself) only produce a network object - they do NOT load a network as Stata variables (see nwload). Many network generators allow the option xvars, which ADDITIONALLY loads the new network as Stata variables right away (equivalent to following the generator with a separate nwload call). Leaving xvars unspecified keeps Stata’s own variable budget free when one deals with many or large networks - all commands that require a netname still work even when no Stata variables for that network exist at all, or after ** drop _all. This also means that one can still deal with larger networks even when using **Small Stata.

Each node in a network also has a node label. This is a unique name for each node. This meta-information can be set with option labs(). As before, there need to be as many entries as there are nodes in the network. When not specified, the program automatically labels nodes according the variables that have been set.

Whenever a network is set with nw2set, it is also made the current network. The current network is always the network that has been most recently loaded or generated. Many nwcommands allow that a netname or a netlist is optional. In case no network is given, all nwcommands generally refer to the current network.

Programmers can use nw2set to write their own import routines (see also nwimport) for different network file formats that are not natively supported by the nwcommands. All you need to do is transform your data either in an adjacency list or an edgelist represented by Stata variables.

From a two-mode network one can also produce a one-mode projection (see nw2project). This basically, collapses the network to use only nodes from either level 1 or level 2.

Supported network types

Two-mode: T1, native - this command’s entire purpose is declaring a two-mode (bipartite) network from a rectangular incidence matrix or a variable list. Binary: yes. Directed: not applicable - two-mode ties are inherently undirected affiliations. Weighted: yes, tie values are accepted and stored as-is. Signed: not checked.

nw2set

Syntax

Description

Remarks

Supported network types

See also

`nw2set`