cross tabulation: convert frequencies to percentages

Hello,

might be rather easy for R pros, but I've been searching to the dead end
to ...

twsource.area <- table(twsource, area, useNA="ifany")

gives me a nice cross tabulation of frequencies of two factors, but now
I want to convert to pecentages of those absolute values. In addition
I'd like an extra column and an extra row with absolute sums. I know,
Excel or the likes will produce it more easily, but how would the
procedure look like in R?

See ?prop.table which is referenced in the See Also section of ?table.

This will give you proportions, so if you want percentages, just
multiply by 100.

To add row and column totals, see ?addmargins which is also in the See
Also for ?table

TAB <- table(state.division, state.region)

TAB

state.region
state.division       Northeast South North Central West
  New England                6     0             0    0
  Middle Atlantic            3     0             0    0
  South Atlantic             0     8             0    0
  East South Central         0     4             0    0
  West South Central         0     4             0    0
  East North Central         0     0             5    0
  West North Central         0     0             7    0
  Mountain                   0     0             0    8
  Pacific                    0     0             0    5

# Overall table proportions

prop.table(TAB)

state.region
state.division       Northeast South North Central West
  New England             0.12  0.00          0.00 0.00
  Middle Atlantic         0.06  0.00          0.00 0.00
  South Atlantic          0.00  0.16          0.00 0.00
  East South Central      0.00  0.08          0.00 0.00
  West South Central      0.00  0.08          0.00 0.00
  East North Central      0.00  0.00          0.10 0.00
  West North Central      0.00  0.00          0.14 0.00
  Mountain                0.00  0.00          0.00 0.16
  Pacific                 0.00  0.00          0.00 0.10


# Column proportions

prop.table(TAB, 2)

state.region
state.division       Northeast     South North Central      West
  New England        0.6666667 0.0000000     0.0000000 0.0000000
  Middle Atlantic    0.3333333 0.0000000     0.0000000 0.0000000
  South Atlantic     0.0000000 0.5000000     0.0000000 0.0000000
  East South Central 0.0000000 0.2500000     0.0000000 0.0000000
  West South Central 0.0000000 0.2500000     0.0000000 0.0000000
  East North Central 0.0000000 0.0000000     0.4166667 0.0000000
  West North Central 0.0000000 0.0000000     0.5833333 0.0000000
  Mountain           0.0000000 0.0000000     0.0000000 0.6153846
  Pacific            0.0000000 0.0000000     0.0000000 0.3846154

addmargins(TAB)

state.region
state.division       Northeast South North Central West Sum
  New England                6     0             0    0   6
  Middle Atlantic            3     0             0    0   3
  South Atlantic             0     8             0    0   8
  East South Central         0     4             0    0   4
  West South Central         0     4             0    0   4
  East North Central         0     0             5    0   5
  West North Central         0     0             7    0   7
  Mountain                   0     0             0    8   8
  Pacific                    0     0             0    5   5
  Sum                        9    16            12   13  50



HTH,

Marc Schwartz