using the magrittr tee %T% operator creates error

Question

I am trying to create two graphs: one of the whole dataset and also a mean graph when split by the "site" grouping factor. Here is the source data: ``` site.data <- structure(list(site = structure(c(1L, 1L, 1L, 1L,1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L), .Label = c("ALBEN", "ALDER", "AMERI"), class = "factor"), year = c(5L, 10L, 20L, 50L, 100L, 200L, 500L, 5L, 10L, 20L, 50L, 100L, 200L, 500L, 5L, 10L, 20L, 50L, 100L, 200L), peak = c(101529.6, 117483.4, 132960.9, 153251.2, 168647.8, 184153.6, 204866.5, 6561.3, 7897.1, 9208.1, 10949.3,12287.6, 13650.2, 15493.6, 43656.5, 51475.3, 58854.4, 68233.3, 75135.9, 81908.3)), .Names = c("site", "year","peak"), class = "data.frame", row.names = c(NA, -20L)) ``` This is my current code: ``` library(ggplot2) library(dplyr) library(magrittr) site.data %T>% # then use a tee operator to plot the graph ggplot(aes(year, peak, color = site)) + geom_line() + geom_point(size = 6) %>% # then group by the site group_by(site) %>% # and…

Accepted Answer

This is a case where order of operations is important. The `%%` operators bind more tightly than `+` does. So when you say

```
site.data %T>% ggplot(aes(year, peak, color = site)) + geom_line() 
```

that's the same as

```
( site.data %T>% ggplot(aes(year, peak, color = site)) ) + geom_line() 
```

which is basically doing

```
site.data + geom_line()
```

which returns the same error you get. You will need to explicitly group all your ggplot layer additions/modifications into a code block. Try

```
site.data %T>%     
{print(ggplot(., aes(year, peak, color = site)) + geom_line() + geom_point(size = 6))}  %>%
group_by(site) %>%  
summarize(mean = mean(peak)) %>%
{ggplot(., aes(site, mean, color = site)) + geom_point(size = 6)}
```

using the magrittr tee %T>% operator creates error

Solution

Problem