Using SQLDF to select specific values from a column - sql

Question

SQLDF newbie here.
I have a data frame which has about 15,000 rows and 1 column.
The data looks like:
cars
autocar
carsinfo
whatisthat
donnadrive
car
telephone
...
I wanted to use the package sqldf to loop through the column and
pick all values which contain "car" anywhere in their value.
However, the following code generates an error.
> sqldf("SELECT Keyword FROM dat WHERE Keyword="car")
Error: unexpected symbol in "sqldf("SELECT Keyword FROM dat WHERE Keyword="car"
There is no unexpected symbol, so I'm not sure whats wrong.
so first, I want to know all the values which contain 'car'.
then I want to know only those values which contain just 'car' by itself.
Can anyone help.
EDIT:
allright, there was an unexpected symbol, but it only gives me just car and not every
row which contains 'car'.
> sqldf("SELECT Keyword FROM dat WHERE Keyword='car'")
Keyword
1 car

Answer 1

Using = will only return exact matches.
You should probably use the like operator combined with the wildcards % or _. The % wildcard will match multiple characters, while _ matches a single character.
Something like the following will find all instances of car, e.g. "cars", "motorcar", etc:
sqldf("SELECT Keyword FROM dat WHERE Keyword like '%car%'")
And the following will match "car" or "cars":
sqldf("SELECT Keyword FROM dat WHERE Keyword like 'car_'")

Answer 2

This has nothing to do with sqldf; your SQL statement is the problem. You need:
dat <- data.frame(Keyword=c("cars","autocar","carsinfo",
"whatisthat","donnadrive","car","telephone"))
sqldf("SELECT Keyword FROM dat WHERE Keyword like '%car%'")
# Keyword
# 1 cars
# 2 autocar
# 3 carsinfo
# 4 car

Answer 3

You can also use regular expressions to do this sort of filtering. grepl returns a logical vector (TRUE / FALSE) stating whether or not there was a match or not. You can get very sophisticated to match specific items, but a basic query will work in this case:
#Using #Joshua's dat data.frame
subset(dat, grepl("car", Keyword, ignore.case = TRUE))
Keyword
1 cars
2 autocar
3 carsinfo
6 car

Answer 4

Very similar to the solution provided by #Chase. Because we do not use subset we do not need a logical vector and can use both grep or grepl:
df <- data.frame(keyword = c("cars", "autocar", "carsinfo", "whatisthat", "donnadrive", "car", "telephone"))
df[grep("car", df$keyword), , drop = FALSE] # or
df[grepl("car", df$keyword), , drop = FALSE]
keyword
1 cars
2 autocar
3 carsinfo
6 car
I took the idea from Selecting rows where a column has a string like 'hsa..' (partial string match)