require(ggplot2)

dat <- iris
dat_setosa <- dat[which(dat$Species=="setosa"),]
dat_versicolor <- dat[which(dat$Species=="versicolor"),]
dat_virginica <- dat[which(dat$Species=="virginica"),]

ggplot(dat_setosa , aes(x=Petal.Length, y=Sepal.Length)) + geom_point()
ggplot(dat_versicolor , aes(x=Petal.Length, y=Sepal.Length)) + geom_point()
ggplot(dat_virginica , aes(x=Petal.Length, y=Sepal.Length)) + geom_point()

dat_setosa_ols <- lm(data=dat_setosa, Petal.Length ~ Sepal.Length)
dat_versicolor_ols <- lm(data=dat_versicolor, Petal.Length ~ Sepal.Length)
dat_virginica_ols <- lm(data=dat_virginica, Petal.Length ~ Sepal.Length)

# beta
dat_setosa_beta <- as.numeric(dat_setosa_ols$coefficients[1])
dat_versicolor_beta <- as.numeric(dat_versicolor_ols$coefficients[1])
dat_virginica_beta <- as.numeric(dat_virginica_ols$coefficients[1])

# r squared
dat_setosa_r2 <- summary(dat_setosa_ols)$r.squared
dat_versicolor_r2 <- summary(dat_versicolor_ols)$r.squared
dat_virginica_r2 <- summary(dat_virginica_ols)$r.squared