Carl,
Are you just looking for the following syntax?
dt[a<35 & b>35, lapply(.SD, median, na.rm = T), by = d]
You can include as many conditions as necessary in `i`. You can also
chain data.tables:
dt[a<35][b>35][, lapply(.SD, median, na.rm = T), by = d]
--Mel.
On 12/9/2015 1:02 PM, carlsutton wrote:
Is there a way to subset a data table using "i" with multiple criteria using
multiple variables(columns)? I have some test code shown below on what I
have tried. And yes, I have read the documentation, taking the data camp
class (Multiple viewing, I'm a slow learner) and have not seen anything
relevant. Also checked for questions on this topic in this forum and did
not find an answer for my query.
Attempting to upload R file
dataTableExamples.R
<http://r.789695.n4.nabble.com/file/n4715347/dataTableExamples.R>
Probably should have stayed in bed today the way things are going.
A cut and paste from RStudio
# Data Table exercises
require(data.table)
a <- seq(2L,40L, by = 4L)
b <- seq(15L,105L,by = 10L)
c <- 1:10L
d <- rep(c(100L,150L),5L)
e <- 101:110L
dt <- data.table(a,b,c,d,e)
dt
dta <- subset(dt, a < 35)
dtb <- subset(dta, b > 35)
dtb
dtb[, lapply(.SD,median), by = d]
# Now attempt to subset the rows in i
vec <- c(a<35, b>35)
dtvec <- dt[vec, lapply(.SD, median, na.rm = TRUE), by = d]
dtvec
And console output
# Now attempt to subset the rows in i
vec <- c(a<35, b>35)
dtvec <- dt[vec, lapply(.SD, median, na.rm = TRUE), by = d]
Error in `[.data.table`(dt, vec, lapply(.SD, median, na.rm = TRUE), by = d)
:
Column 1 of result for group 2 is type 'double' but expecting type
'integer'. Column types must be consistent for each group.
dtvec
a b c d e
1: 2 15 1 100 101
2: 6 25 2 150 102
3: 10 35 3 100 103
4: 14 45 4 150 104
5: 18 55 5 100 105
6: 22 65 6 150 106
7: 26 75 7 100 107
8: 30 85 8 150 108
9: 34 95 9 100 109
10: NA NA NA NA NA
11: NA NA NA NA NA
12: NA NA NA NA NA
13: NA NA NA NA NA
14: NA NA NA NA NA
15: NA NA NA NA NA
16: NA NA NA NA NA
The error message has me confused.
/Column 1 of result for group 2 is type/
What group 2? I have only grouped on column "d". Result 1 is ???? No idea
what "result 1" is referring to, is it the subset in "i", the median of col
a?? No clue.
I have only created integer variable for the data table, so why the
rejection " Column 1 of result for group 2 is type 'double' but expecting
type 'integer'. Column types must be consistent for each group." What
double? I have not created any double numbers.
Carl Sutton
-----
Carl Sutton
--
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http://r.789695.n4.nabble.com/subset-data-table-in-i-with-multiple-criteria-for-multiple-variables-tp4715347.html
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