r - How to remove rows that have only 1 combination for a given ID

Question

I have a dataframe like this

ID <- c("A","A","A","B","B","C","C")
Measurement <- c ("Length","Breadth","Breadth","Breadth","Length","Length","Length")  
Value <- c(4.5,6.6,7.5,3.3,5.6,8.9,16.1)
df <- data.frame(ID,Measurement,Value)
df

  ID Measurement Value
1  A      Length   4.5
2  A     Breadth   6.6
3  A     Breadth   7.5
4  B     Breadth   3.3
5  B      Length   5.6
6  C      Length   8.9
7  C      Length  16.1

My desired output is

  ID Measurement Value
1  A      Length   4.5
2  A     Breadth   6.6
3  A     Breadth   7.5
4  B     Breadth   3.3
5  B      Length   5.6

I want to remove rows that have only 1 combination for a given ID.

I do something like this to remove rows in a dataframe that has only 1 column with 1 unique value.

df_count <- length(unique(df$Measurement))
    if(df_count < 2)
      next

I am trying to extend that to use in a data frame that has a combination of 2 columns and I am not able to use the same logic. Please help with some inputs on how to solve this

Answer 1

In dplyr, it would be

library(dplyr)

df %>% group_by(ID) %>% filter(n_distinct(Measurement) > 1)
##       ID Measurement Value
##   <fctr>      <fctr> <dbl>
## 1      A      Length   4.5
## 2      A     Breadth   6.6
## 3      A     Breadth   7.5
## 4      B     Breadth   3.3
## 5      B      Length   5.6