nwfromedge

Imports network data from edgelist

Syntax

nwfromedge 
 fromid
 toid
[tievalue]
[if]
[,
name(newnetname)
xvars
labs(lab1 lab2 ...)
undirected
directed
twomode]

name(newnetname)	name of the new network; default = network
xvars	generate Stata variables for the network
labs(lab1 lab2 …)	overwrite node labels
undirected	force the network to be undirected (alias: forceundirected)
directed	force the network to be directed (alias: forcedirected)
twomode	declare a two-mode (bipartite) network instead - fromid/toid are the mode-1/mode-2 id variables, not a directed ego/alter pair. An exact alias for nw2fromedge, forwarding name()/xvars only; cannot be combined with directed/undirected/forcedirected/forceundirected. See nw2fromedge for the full two-mode-specific behavior (same-label disambiguation, mode assignment, project())
noclear	do not clear existing dataset
replace	if a network named newnetname already exists, drop it and use this name anyway (see nwset for the same convention)
labprefix(string)	prefix used for auto-generated node labels when fromid/toid are numeric and labs() is not specified; default = n - named labprefix(), not prefix(), to avoid colliding with nwrecode’s unrelated prefix() (which prefixes new network names, not node labels)
overwrite	forwarded to nwload governing whether this command’s own generated Stata variables overwrite existing ones of the same name - unrelated to replace above, which is about the network, not Stata variables

Description

nwfromedge imports a network from a dataset in edgelist format.

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, the data

• hline 14c -

• c	fromid toid c

• hline 14c -

• 1. c

     1 2 c

• 1. c

     2 3 c

• 1. c

     4 2 c

• hline 14c -

stores information about three ties (1=>2), (2=>3) and (4=>2) among four unique network nodes. The variables defining the edges can also be string variables.

• hline 25c -

• c	fromid toid valuec

• hline 25c -

• 1. c	Peter Thomas 1 c

• 1. c	Tim Peter 3 c

• 1. c	Mathilde Thomas 2 c

• hline 25c -

Here, there are also three relationships: (Peter => Thomas), (Tim => Peter) and (Mathilde => Thomas).

The following command declares such data as network data:

. nwfromedge fromid toid value, name(mynet)

This automatically generates the relevant meta-information for the network and makes it available for other programs under the netname mynet. In case no name() is specified, the command tries to come up with a suitable name for the new network. By default, it tries network, however, if a network with this name already exists, it comes up with an alternative name network_1 and so on (see nwvalidate).

After a network has been declared, one can refer to it by its netname, just as if one would refer to a varname. For example, this makes a network plot of mynet.

. nwplot mynet

Or alternatively, this calculates the betweenness centrality of the nodes in mynet.

. nwbetween mynet

By default, nwfromedge recognizes if a network is directed or undirected, i.e. for each dyad entry (i,j) there is also a dyad entry (j,i). However, this automatic detection can be overwritten with the options undirected and directed.

One can also transfrom any network that exists in memory into such an edgelist with nwtoedge.

Examples

This loads a network dataset from the internet and transforms the network glasgow1 into an edgelist.

. nwwebuse glasgow, nwclear
. nwtoedge glasgow1

nwtoedge produces variables _ego/_alter (not _fromid/_toid) plus a tie-value column named after the network itself (glasgow1 here, not _link) - and, being every possible pair rather than a compact edgelist, it needs filtering down to the real ties before being turned back into a network:

. keep if glasgow1 == 1
. nwfromedge _ego _alter, name(mynet)

glasgow1 has 50 nodes but only 47 with at least one tie; mynet still comes out with all 50 - the 3 isolates nwtoedge could not write as edgelist rows are added back automatically, with no extra step needed (see this file’s own Supported network types section above). This only works because nwtoedge itself produced this particular edgelist; it would not apply to an edgelist typed in by hand or imported from an external source.

Supported network types

Binary: yes. Directed: yes, via directed/undirected/forcedirected/forceundirected. Weighted: yes - a third edge-list column supplies tie values. Signed: not checked. Two-mode: yes, via twomode - an exact alias for nw2fromedge, the command that actually implements two-mode edge-list import (see that command’s own help file for the full behavior, where isolate preservation below does not apply). A node with zero ties (an isolate) can never appear as a ROW in an edgelist - there is no pair to write - but a round trip through nwtoedge specifically is not affected: nwtoedge attaches its source network’s own full node list to the edgelist dataset (invisibly - no extra variables or rows), and nwfromedge automatically adds back any node that list has but the edgelist’s own ties did not reproduce. A hand-built or externally-sourced edgelist carries no such list, so isolates neither of those every had are genuinely unrepresentable - add them with nwaddnodes same as always.