dplyr's filter function: how to return every value (or «cancel» the effect of filter)?

Question

This may seem like a weird question, but is there a way to pass a value to filter() that basically does nothing?

data(cars)
library(dplyr)
cars %>% filter(speed==`magic_value_that_returns_cars?`)

And you'd get the whole data frame cars back. I'm thinking that this could be useful in a shiny application, where the user would just need to choose the values he wants to filter by; for example the user could choose "Europe", "Africa" or "America" and behind the scenes thet data frame would get filtered and then a table with descriptive statistics for "Europe" would be returned (if the user chose "Europe"). But what if the user wants to have descriptive statistics without first filtering? Is there a value that we could pass to filter to «cancel» filter and pass the whole dataframe to summarise()?

Answer 1

The column will always be equal to itself, so

cars %>% filter(speed == speed)

will return the full data set.

Update: Turns out that won't work when there are NA values in the data. Sorry I missed that. So, to make this answer correct I will urge you go with the recommendation of @konvas from the comments.

cars %>% filter(TRUE)

Of course there are other ways, but I think this is the best.

Answer 2

If you're applying this in a shiny application, here's an example of how you can filter by "nothing" if for instance, a user selects "All". The combined use of braces and if else will effectively allow you to skip the line where you apply filter to the data set:

x <- "All"

cars %>%
  {if(x!="All") filter(.,speed==x) else .} %>%
  head()

# speed dist
# 1     4    2
# 2     4   10
# 3     7    4
# 4     7   22
# 5     8   16
# 6     9   10

# No data is filtered

x <- 7

cars %>%
{if(x!="All") filter(.,speed==x) else .} %>%
  head()

# speed dist
# 1     7    4
# 2     7   22

# The data is filtered by x==7