count combined occurrences of categories

Dear all,

i would like to count the number of times where I have combined occurrences of the categories of 2 variables.

For instance, in the dataframe below, i would like to know how many times each author (au1, au2, au3 represent the first, second, third author) is associated with each of the category of the variable 'nam'. The position of the author does not matter.

nam <- c('da', 'ya', 'da', 'da', 'fr', 'fr', 'fr', 'da', 'ya', 'fr')
au1 <- c('deb', 'art', 'deb', 'seb', 'deb', 'deb', 'mar', 'mar', 'joy', 'joy')
au2 <- c('art', 'deb', 'mar', 'deb', 'joy', 'mar', 'art', 'lio', 'nem', 'mar')
au3 <- c('mar', 'lio', 'joy', 'mar', 'art', 'lio', 'nem', 'art', 'deb', 'tat')
tutu <- data.frame(cbind(nam, au1, au2, au3))

thanks,

David
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