This function tries to replicate the information contained in the original
file distributed by The Correlates of War Project (dyadic_format3.dta).
That file is not included in this package due to its size.
The result is a data.frame containing the common years of
the states selected via country1, country2, year by rows.
An additional column dyadid, computed as (1000*ccode1)+ccode2 is provided
in order to identify relationships.
For each IGO selected via ioname (or all if the default option has been
used) a column (using lowercase ioname as identifier) is provided with the
following code system:
| Category | Numerical Value |
| No Joint Membership | 0 |
| Joint Full Membership | 1 |
| Missing data | -9 |
| State Not System Member | -1 |
See igo_recode_dyadic() section for an easy way to recode the numerical
values into factors.
If one state in an IGO is a full member but the other is an associate member
or observer, that IGO is not coded as a joint membership.