I have time-series data on approval ratings of British Prime Ministers.  The
prime ministers dating from MacMillan onward till today are coded as dummy
variables and the approval ratings are entered for each month.  I want to
know the mean value of the approval rating of each Prime Minister in the
dataset and the approval rating during his/her first month and last month as
PM.  What R code should I enter for these data?  In other words, I want hold
the dummy corresponding to each Prime Minister fixed at value one and know
the first rating that PM has, the last rating s/he has, and the mean rating
s/he has.  Thanks.

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