How to find a column value based on the unique value for another column

Question

I have the following dataset:

Class     Value
A         5.4
A         5.4
A         5.4
B         3.6
B         2.7
C         4.02
C         4.02
C         4.02
D         6.33
D         6.33

What I want is to retrieve only the classes that have similar values, which in this case should return the class A and D but not, for example, the class B since it has two different values.

To do that, I tried the following:

sub <- dataset[as.logical(ave(dataset$Value, dataset$Class, FUN = function(x) all(x==x))), ]

But this returns all the classes which I don't want.

Can someone help me with that?

BENY · Accepted Answer · 2019-01-18 20:29:05Z

3

Using aggregate with number of unique (length(unique))

filterdf=aggregate(Value ~ Class, df, function(x) length(unique(x)))
df[df$Class%in%filterdf[filterdf$Value==1,]$Class,]
   Class Value
1      A  5.40
2      A  5.40
3      A  5.40
6      C  4.02
7      C  4.02
8      C  4.02
9      D  6.33
10     D  6.33

Alternative from markus

idx <- with(df, ave(Value, Class, FUN = function(x) length(unique(x))) == 1)
df[idx, ]

edited Jan 18, 2019 at 20:29

answered Jan 18, 2019 at 20:17

BENY

324k22 gold badges176 silver badges250 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

markus Over a year ago

I was about to post a similar solution using ave which you might want to add as alternative. idx <- with(df, ave(Value, Class, FUN = function(x) length(unique(x))) == 1); df[idx, ]

BENY Over a year ago

@markus that is great thank you :-) , if you would like convert it as an answer I will definitively upvote for you man

markus Over a year ago

That is kind of you. I found it too similiar to what you posted 1 minute earlier. Feel free to use it.

tmfmnk · Accepted Answer · 2019-01-18 21:25:23Z

0

With tidyverse you can do:

df %>%
 group_by(Class) %>%
 filter(all(Value == first(Value)))

Or:

df %>%
 group_by(Class) %>%
 filter(n_distinct(Value) == 1)

Or:

df %>%
 group_by(Class) %>%
 filter(all(Value %/% first(Value) != 0))

Or:

df %>%
 group_by(Class, Value) %>%
 mutate(temp = seq_along(Value)) %>%
 group_by(Class) %>%
 filter(sum(temp[temp == 1]) == 1) %>%
 select(-temp)

Or basically the same as the post from @W-B:

df %>%
 group_by(Class) %>%
 filter(length(unique(Value)) == 1)

edited Jan 18, 2019 at 21:25

answered Jan 18, 2019 at 21:00

tmfmnk

40.4k4 gold badges54 silver badges73 bronze badges

Collectives™ on Stack Overflow

How to find a column value based on the unique value for another column

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related