Name A B C
apple 1 -1 0
banana 2 -2 1
pear -3 0 1

df[-1] <- sign(df[-1]) * -1

df
#    Name  A B  C
#1  apple -1 1  0
#2 banana -1 1 -1
#3   pear  1 0 -1

df <- structure(list(Name = structure(1:3, .Label = c("apple", "banana",
"pear"), class = "factor"), A = c(-1, -1, 1), B = c(1, 1, 0),
C = c(0, -1, -1)), .Names = c("Name", "A", "B", "C"), row.names = c(NA,
-3L), class = "data.frame")