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

Question

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.

Answer 1

Use which(mydata_2$height_chad1 == 2585)

Short example

df <- data.frame(x = c(1,1,2,3,4,5,6,3),                  y = c(5,4,6,7,8,3,2,4)) df   x y 1 1 5 2 1 4 3 2 6 4 3 7 5 4 8 6 5 3 7 6 2 8 3 4  which(df$x == 3) [1] 4 8  length(which(df$x == 3)) [1] 2  count(df, vars = "x")   x freq 1 1    2 2 2    1 3 3    2 4 4    1 5 5    1 6 6    1  df[which(df$x == 3),]   x y 4 3 7 8 3 4 

As Matt Weller pointed out, you can use the length function. The count function in plyr can be used to return the count of each unique column value.

Answer 2

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