I'm brand new to R, so this might be obvious. 

The code I have so far:

```
rm(list=ls())

kdata = read.table("data_fra_klassen_v20.txt",header = TRUE,)

library(openxlsx)

kdata = read.xlsx("data_fra_klassen_v20.xlsx") 

head(kdata)

```

Here is the dataset: 

```
  gender    shoe    height  colour
  Man        43      176    Green
  Woman      36      166    Brown
  Man        43      182    Other
  Man        36      151    Brown
  Woman      43      183    Blue
  Man        44      184    Blue
  Woman      38      164    Brown
  Woman      37      160    Brown
  Man        41      175    Brown

```

I'm trying to find the mean, and median within each gender. 

I was thinking maybe something like this: 

```
heightmen = kdata$height[kdata$gender=="Man"]
mean(heightmen)

```

However, it seems like it can't find any values.