Saving rows of a data frame based on the values of a column of another data frame

Question

I have a dataframe with 50 rows and 10 columns and another with 10 rows and 5 columns, with the first column of both dataframes can have equal values. How do I select and save the rows, only, from the first data frame following the condition that should be equal to the rows (from the first column) of the second data frame?

Answer 1

created two dataframe to exemplify

A <- data.frame(X = sample(LETTERS, 50, rep = T), Y = rnorm(50), Z = rpois(50, 3))
B <- data.frame(X1 = sample(LETTERS, 10, rep = T), Y1 = rnorm(10))

for you to pick up the lines from the first column of A which have equal values in the rows in the first column of B, you can use the command below. I saved in a dataframe C

C <- A[which(A$X %in% B$X1),]