[R] What does the : operator mean in glm formulas

[(Ted Harding)]

On 19-Jan-2012 Xiaobo Gu wrote:
> Hi,
> I see the following is the credit scoreing in R guide :
> 
> m2<-glm(formula = good_bad ~ checking + duration + history +
> purpose +amount + savings + employed + installp + marital +
> coapp +age + other + depends + telephon + foreign +checking:amount
> 
> What does checking:amount mean?
> 
> Regards,
> Xiaobo Gu

See the explanation of model formulae under "Details" in ?glm :

  A specification of the form ?first:second? indicates
  the set of terms obtained by taking the interactions
  of all terms in 'first' with all terms in 'second'.
  The specification 'first*second' indicates the _cross_
  of 'first' and 'second'.
  This is the same as 'first + second + first:second'.

Ted.

-------------------------------------------------
E-Mail: (Ted Harding) <Ted.Harding at wlandres.net>
Date: 19-Jan-2012  Time: 13:37:23
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