Replace characters from a column of a data frame R

Use gsub:

data1$c <- gsub('_', '-', data1$c)data1            a b   c1  0.34597094 a A-B2  0.92791908 b A-B3  0.30168772 c A-B4  0.46692738 d A-B5  0.86853784 e A-C6  0.11447618 f A-C7  0.36508645 g A-C8  0.09658292 h A-C9  0.71661842 i A-C10 0.20064575 j A-C

If your variable data1$c is a factor, it's more efficient to change the labels of the factor levels than to create a new vector of characters:

levels(data1$c) <- sub("_", "-", levels(data1$c))            a b   c1  0.73945260 a A-B2  0.75998815 b A-B3  0.19576725 c A-B4  0.85932140 d A-B5  0.80717115 e A-C6  0.09101492 f A-C7  0.10183586 g A-C8  0.97742424 h A-C9  0.21364521 i A-C10 0.02389782 j A-C

You can use the stringr library:

library('stringr')a <- runif(10)b <- letters[1:10]c <- c(rep('A-B', 4), rep('A_B', 6))data <- data.frame(a, b, c)data#             a b   c# 1  0.19426707 a A-B# 2  0.12902673 b A-B# 3  0.78324955 c A-B# 4  0.06469028 d A-B# 5  0.34752264 e A_C# 6  0.55313288 f A_C# 7  0.31264280 g A_C# 8  0.33759921 h A_C# 9  0.72322599 i A_C# 10 0.25223075 j A_Cdata$c <- str_replace_all(data$c, '_', '-')data#             a b   c# 1  0.19426707 a A-B# 2  0.12902673 b A-B# 3  0.78324955 c A-B# 4  0.06469028 d A-B# 5  0.34752264 e A-C# 6  0.55313288 f A-C# 7  0.31264280 g A-C# 8  0.33759921 h A-C# 9  0.72322599 i A-C# 10 0.25223075 j A-C

Note that this does change factored variables into character.