How to get row index number in R?

Question

Suppose I have a list or data frame in R, and I would like to get the row index, how do I do that? That is, I would like to know how many rows a certain matrix consists of.

Answer 1

I'm interpreting your question to be about getting row numbers.

• You can try as.numeric(rownames(df)) if you haven't set the rownames. Otherwise use a sequence of 1:nrow(df).
• The which() function converts a TRUE/FALSE row index into row numbers.

Answer 2

It not quite clear what exactly you are trying to do.

To reference a row in a data frame use df[row,]

To get the first position in a vector of something use match(item,vector), where the vector could be one of the columns of your data frame, eg df$cname if the column name is cname.

Edit:

To combine these you would write:

df[match(item,df$cname),]

Note that the match gives you the first item in the list, so if you are not looking for a unique reference number, you may want to consider something else.