[r] Return row number(s) for a particular value in a column in a dataframe

I have a data frame (df) and I was wondering how to return the row number(s) for a particular value (2585) in the 4th column (height_chad1) of the same data frame?

I've tried:

row(mydata_2$height_chad1, 2585)

and I get the following error:

Error in factor(.Internal(row(dim(x))), labels = labs) : 
  a matrix-like object is required as argument to 'row'

Is there an equivalent line of code that works for data frames instead of matrix-like objects?

Any help would be appreciated.

which(df==my.val, arr.ind=TRUE)