Use an example to do this:
> dput(data) structure(list(mpg = c(15.2, 10.4, 13.3, 14.7, 22.8, 15.5, 14.3, 19.7, 32.4, 27.3, 15.8, 30.4, 21.4, 18.7, 10.4, 30.4, 15, 21, 21, 22.8, 24.4, 19.2, 17.8, 16.4, 17.3, 15.2, 19.2, 26, 33.9, 21.5, 18.1, 21.4), cyl = c(8, 8, 8, 8, 4, 8, 8, 6, 4, 4, 8, 4, 6, 8, 8, 4, 8, 6, 6, 4, 4, 6, 6, 8, 8, 8, 8, 4, 4, 4, 6, 4), disp = c(304, 472, 350, 440, 108, 318, 360, 145, 78.7, 79, 351, 75.7, 258, 360, 460, 95.1, 301, 160, 160, 140.8, 146.7, 167.6, 167.6, 275.8, 275.8, 275.8, 400, 120.3, 71.1, 120.1, 225, 121), hp = c(150, 205, 245, 230, 93, 150, 245, 175, 66, 66, 264, 52, 110, 175, 215, 113, 335, 110, 110, 95, 62, 123, 123, 180, 180, 180, 175, 91, 65, 97, 105, 109), drat = c(3.15, 2.93, 3.73, 3.23, 3.85, 2.76, 3.21, 3.62, 4.08, 4.08, 4.22, 4.93, 3.08, 3.15, 3, 3.77, 3.54, 3.9, 3.9, 3.92, 3.69, 3.92, 3.92, 3.07, 3.07, 3.07, 3.08, 4.43, 4.22, 3.7, 2.76, 4.11 ), wt = c(3.435, 5.25, 3.84, 5.345, 2.32, 3.52, 3.57, 2.77, 2.2, 1.935, 3.17, 1.615, 3.215, 3.44, 5.424, 1.513, 3.57, 2.62, 2.875, 3.15, 3.19, 3.44, 3.44, 4.07, 3.73, 3.78, 3.845, 2.14, 1.835, 2.465, 3.46, 2.78), qsec = c(17.3, 17.98, 15.41, 17.42, 18.61, 16.87, 15.84, 15.5, 19.47, 18.9, 14.5, 18.52, 19.44, 17.02, 17.82, 16.9, 14.6, 16.46, 17.02, 22.9, 20, 18.3, 18.9, 17.4, 17.6, 18, 17.05, 16.7, 19.9, 20.01, 20.22, 18.6), vs = c(0, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1), am = c(0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1), gear = c(3, 3, 3, 3, 4, 3, 3, 5, 4, 4, 5, 4, 3, 3, 3, 5, 5, 4, 4, 4, 4, 4, 4, 3, 3, 3, 3, 5, 4, 3, 3, 4), carb = c(2, 4, 4, 4, 1, 2, 4, 6, 1, 1, 4, 2, 1, 2, 4, 2, 8, 4, 4, 2, 2, 4, 4, 3, 3, 3, 2, 2, 1, 1, 1, 2), car = structure(c(18L, 19L, 5L, 13L, 14L, 31L, 7L, 21L, 20L, 22L, 23L, 24L, 25L, 26L, 2L, 15L, 4L, 9L, 12L, 29L, 30L, 6L, 1L, 3L, 27L, 10L, 28L, 16L, 11L, 8L, 17L, 32L), .Label = c("AMC Javelin, AMC Javelin, AMC Javelin, AMC Javelin, AMC Javelin", "Cadillac Fleetwood", "Camaro Z28", "Chrysler Imperial", "Datsun 710, Datsun 710, Datsun 710, Datsun 710", "Dodge Challenger", "Duster 360", "Ferrari Dino, Ferrari Dino, Ferrari Dino, Ferrari Dino, Ferrari Dino", "Fiat 128, Fiat 128, Fiat 128, Fiat 128, Fiat 128", "Fiat X1-9", "Ford Pantera L", "Honda Civic, Honda Civic, Honda Civic, Honda Civic, Honda Civic", "Hornet 4 Drive, Hornet 4 Drive, Hornet 4 Drive, Hornet 4 Drive, Hornet 4 Drive", "Hornet Sportabout", "Lincoln Continental", "Lotus Europa", "Maserati Bora", "Mazda RX4", "Mazda RX4 Wag, Mazda RX4 Wag, Mazda RX4 Wag, Mazda RX4 Wag, Mazda RX4 Wag", "Merc 230", "Merc 240D", "Merc 280", "Merc 280C", "Merc 450SE", "Merc 450SL", "Merc 450SLC", "Pontiac Firebird", "Porsche 914-2", "Toyota Corolla", "Toyota Corona", "Valiant", "Volvo 142E" ), class = "factor")), .Names = c("mpg", "cyl", "disp", "hp", "drat", "wt", "qsec", "vs", "am", "gear", "carb", "car"), row.names = c("Mazda RX4", "Mazda RX4 Wag", "Datsun 710", "Hornet 4 Drive", "Hornet Sportabout", "Valiant", "Duster 360", "Merc 240D", "Merc 230", "Merc 280", "Merc 280C", "Merc 450SE", "Merc 450SL", "Merc 450SLC", "Cadillac Fleetwood", "Lincoln Continental", "Chrysler Imperial", "Fiat 128", "Honda Civic", "Toyota Corolla", "Toyota Corona", "Dodge Challenger", "AMC Javelin", "Camaro Z28", "Pontiac Firebird", "Fiat X1-9", "Porsche 914-2", "Lotus Europa", "Ford Pantera L", "Ferrari Dino", "Maserati Bora", "Volvo 142E"), class = "data.frame")
As you can see, we have some duplicated words in the car column. I would like to leave only one word / phrase in each cell. In my original data, words are also separated by a coma. It is possible that in my source data I have the same word in another column, and I would like to leave it as it is. The function should only be used for this particular column.