how subset a data frame by the column using a character string

Question

I have a data frame in R like this:

> df <- data.frame(cbind(C.01=1, C.02=1:8, C.03=c("A","B","C","D","E","F","G","H")))

And I would obtain a subset like this:

> subset(df, C.03 == "A")

C.01 C.02 C.03
1    1    1    A

It's possible do the same subset but having the name of the column in xx <- "C.03" ??

Because subset(df, xx == "A") doesn't works.

Thnks.

Avoid using subset and use standard [ and [[ operators, like @DavidArenburg suggests. Also df[df[[xx]]=="A",] works in this case. — nicola
– nicola, Commented Apr 21, 2015 at 10:59
possible duplicate of how to extract a subset of a data frame based on a condition involving a field? — rmuc8
– rmuc8, Commented Apr 21, 2015 at 11:25
stackoverflow.com/questions/29540658/r-how-to-make-a-subtable/… just remember to put the string in quotation marks ".." — rmuc8
– rmuc8, Commented Apr 21, 2015 at 11:27
I would strongly advise to use either David's or nicola's solution but, if you really want to use subset, you could try subset(df,eval(parse(text=paste0(xx,"==","\"A\"")))). However, this kind of hacky code ultimately eliminates subset's main advantage of better readability. Using subset might also cause unexpected behaviour (see, e.g., stackoverflow.com/questions/9860090/…). — cryo111
– cryo111, Commented Apr 21, 2015 at 12:59

Phil · Accepted Answer · 2015-04-21 14:13:39Z

3

Using base R (thanks @David Arenburg):

df[df[xx] == "A", ]

Or with dplyr, which I suggest because the syntax is easier to make sense of:

require("dplyr")
df <- filter(df, C.03 == "A")

answered Apr 21, 2015 at 14:13

Phil

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