Extracting part of a factor
You mean this? test$place <- factor(test$place) You can create a new column in a data frame by assigning something to it. E.g. test$pollywog <- 1:6 ... creates that column in "test". But factor(test$place) was empty, because no such column previously existed, like: R > factor(test$barbapapa) factor(0) Levels: So the right hand side has 0 rows, but the left hand side needs six. Of course you could create your column directly: R > str(test) 'data.frame': 6 obs. of 6 variables: $ subject: Factor w/ 6 levels "001-002","002-003",..: 1 2 3 4 5 6 $ group : Factor w/ 2 levels "boys","girls": 1 1 1 2 2 2 $ wk1 : int 2 7 9 5 2 1 $ wk2 : int 3 6 4 7 6 4 $ wk3 : int 4 5 6 8 3 7 $ wk4 : int 5 4 1 9 8 4 R > test$place <- factor(substr(test$subject,1,3)) # here's were it gets done R > str(test) 'data.frame': 6 obs. of 7 variables: $ subject: Factor w/ 6 levels "001-002","002-003",..: 1 2 3 4 5 6 $ group : Factor w/ 2 levels "boys","girls": 1 1 1 2 2 2 $ wk1 : int 2 7 9 5 2 1 $ wk2 : int 3 6 4 7 6 4 $ wk3 : int 4 5 6 8 3 7 $ wk4 : int 5 4 1 9 8 4 $ place : Factor w/ 6 levels "001","002","003",..: 1 2 3 4 5 6 ... it's just that you insisted on mutate(). Cheers, Boris
On Mar 4, 2016, at 9:31 PM, KMNanus <kmnanus at gmail.com> wrote:
Boris - Boy, do I feel dumb - that?s exactly what I wanted. I?ve tried this every way I can think of without assigning the result to the original name of the data frame. I was trying to assign the result to a variable (test$place). Can u pls explain to me why assigning the result to the new variable was wrong? BTW, really appreciate your help. Ken kmnanus at gmail.com 914-450-0816 (tel) 347-730-4813 (fax) <image001.jpg>
On Mar 4, 2016, at 9:21 PM, Boris Steipe <boris.steipe at utoronto.ca> wrote: LOL you still need to assign it though: test <- mutate(test, place = factor(substr(test$subject,1,3))) str(test) 'data.frame': 6 obs. of 7 variables: $ subject: Factor w/ 6 levels "001-002","002-003",..: 1 2 3 4 5 6 $ group : Factor w/ 2 levels "boys","girls": 1 1 1 2 2 2 $ wk1 : int 2 7 9 5 2 1 $ wk2 : int 3 6 4 7 6 4 $ wk3 : int 4 5 6 8 3 7 $ wk4 : int 5 4 1 9 8 4 $ place : Factor w/ 6 levels "001","002","003",..: 1 2 3 4 5 6 Without assigning the result, the output only gets printed to console. Remember that R is a functional language - a properly written R functio does not change anything, it only returns its result. :-) On Mar 4, 2016, at 4:13 PM, KMNanus <kmnanus at gmail.com> wrote:
If I call mutate this way - mutate(test, place = factor(substr(test$subject,1,3))), I get the same output as above but when I call class(test$place), I get NULL and the variable disappears.