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# R/dplyr: Extracting Data Frame Column Value for Filtering With %in%

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I’ve been playing around with dplyr over the weekend and wanted to extract the values from a data frame column to use in a later filtering step.

```library(dplyr)
df = data.frame(userId = c(1,2,3,4,5), score = c(2,3,4,5,5))```

And wanted to extract the userIds of those people who have a score greater than 3. I started with:

```highScoringPeople = df %>% filter(score > 3) %>% select(userId)
> highScoringPeople
userId
1      3
2      4
3      5```

And then filtered the data frame expecting to get back those 3 people:

```> df %>% filter(userId %in% highScoringPeople)
[1] userId score
<0 rows> (or 0-length row.names)```

No rows! I created vector with the numbers 3-5 to make sure that worked:

```> df %>% filter(userId %in% c(3,4,5))
userId score
1      3     4
2      4     5
3      5     5```

That works as expected so highScoringPeople obviously isn’t in the right format to facilitate an ‘in lookup’. Let’s explore:

```> str(c(3,4,5))
num [1:3] 3 4 5

> str(highScoringPeople)
'data.frame': 3 obs. of  1 variable:
\$ userId: num  3 4 5```

Now it’s even more obvious why it doesn’t work – highScoringPeople is still a data frame when we need it to be a vector/list.

One way to fix this is to extract the userIds using the \$ syntax instead of the select function:

```highScoringPeople = (df %>% filter(score > 3))\$userId

> str(highScoringPeople)
num [1:3] 3 4 5

> df %>% filter(userId %in% highScoringPeople)
userId score
1      3     4
2      4     5
3      5     5```

Or if we want to do the column selection using dplyr we can extract the values for the column like this:

```highScoringPeople = (df %>% filter(score > 3) %>% select(userId))[[1]]

> str(highScoringPeople)
num [1:3] 3 4 5```

Not so difficult after all.

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