Hi R-Experts,
I have a data.frame like this:
> head(map)
chr snp poscm posbp dist
1 1 M1 2.99043 3249189 NA
2 1 M2 3.06457 3273096 0.07414
3 1 M3 3.17018 3307151 0.10561
4 1 M4 3.20892 3319643 0.03874
5 1 M5 3.28120 3342947 0.07228
6 1 M6 3.29624 3347798 0.01504
I need to split this into chunks of 250 rows (there will usually be a last
chunk with < 250 rows).
If I only had to extract one 250-line chunk, it would be easy:
map1 <- map[1:250, ]
or using subset().
I tried to make it a loop iterating through num and using beg and nd for
starting and ending indices, but I couldn’t figure out how to reference all the
variables I needed in this:
> chunks
beg nd let num
1 1 250 a 1
2 251 500 b 2
3 501 750 c 3
4 751 1000 d 4
5 1001 1250 e 5
6 1251 1500 f 6
7 1501 1750 g 7
8 1751 2000 h 8
9 2001 2250 i 9
10 2251 2500 j 10
…
Remembering that loops are not always the best answer in R, I looked at other
options like split, following this example but not being able to adapt it from
a vector to a data.frame version
http://stackoverflow.com/questions/3318333/split-a-vector-into-chunks-in-r
<http://stackoverflow.com/questions/3318333/split-a-vector-into-chunks-in-r>
(Yes, I’ve reviewed the language documentation). I checked out ddply and
data.table, but couldn’t find a way to use them with index positions instead of
column values.
Thanks,
Liz
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