r - How to subset a dataframe based on another dataframe

Question

I have data dat like this:

s    A     chan
10   0.1   1
20   0.2   1
30   0.3   1
40   0.5   1
50   0.7   1
60   0.5   1
10   0.1   2
20   0.3   2
30   0.4   2
40   0.5   2
50   0.6   2
60   0.6   2
10   0.2   3
20   0.2   3
30   0.3   3
40   0.4   3
50   0.5   3
40   0.7   3
10   0.2   4
20   0.2   4
30   0.3   4
40   0.3   4
50   0.6   4
60   0.8   4

and I want to subset my data frame dat based on s (time) for each chan (channel) with a data frame df like this

If I use dat %>% filter(s %in% df$s) I get each value for every channel like this:

s    A     chan
10   0.1   1
20   0.2   1
30   0.3   1
40   0.5   1
10   0.1   2
20   0.3   2
30   0.4   2
40   0.5   2
10   0.2   3
20   0.2   3
30   0.3   3
40   0.4   3
10   0.2   4
20   0.2   4
30   0.3   4
40   0.3   4

but what I actualy want it this:

s    A     chan
10   0.1   1
20   0.3   2
30   0.3   3
40   0.3   4

How can I achieve this result?

ok, in this case it would acutally work, I should have used differnt numbers for s. — user18046926
– user18046926, Commented Jan 27, 2022 at 12:38

barpapapa · Accepted Answer · 2022-01-28 00:00:39Z

2

what you are looking for is semi_join; it filters rows from left data frame based on the presence or absence of matches in right data frame,

semi_join(dat, df, by = c("s", "chan"))

answered Jan 28, 2022 at 0:00

barpapapa

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user18046926 Over a year ago

That does the trick with my test data, thanks a lot!

Valentia · Accepted Answer · 2022-01-27 12:47:56Z

0

I think this should do it

dat[which(dat[,3]==df[1:4,2] & dat[,1]==df[1:4,1]),]

1:4 being the range of lines in df.

answered Jan 27, 2022 at 12:47

Valentia

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