Hello,
Inline.
Em 28-08-2012 18:23, Nordlund, Dan (DSHS/RDA) escreveu:
-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of Norbert Skalski
Sent: Tuesday, August 28, 2012 9:49 AM
To: r-help at r-project.org
Subject: [R] date in plot, can't add regression line
Hello all,
I have been using R for about 3 weeks and I am frustrated by a problem.
I have read R in a nutshell, scoured the internet for help but I either
am not understanding examples or am missing something completely basic.
Here is the problem:
I want to plot data that contains dates on the x axis. Then I want to
fit a line to the data. I have been unable to do it.
This is an example of the data (in a dataframe called
"tradeflavorbyday"), 40 lines of it (I'm sorry it's not in a runnable
form, not sure how to get that from R) :
tradeflavor timestamp x
1 1 2009-01-22 1
2 2 2009-01-22 1
3 1 2009-01-23 1
4 1 2009-01-27 54
5 1 2009-01-28 105
6 2 2009-01-28 2
7 16 2009-01-28 2
8 1 2009-01-29 71
9 16 2009-01-29 2
10 1 2009-01-30 42
11 1 2009-02-02 19
12 16 2009-02-02 2
13 1 2009-02-03 36
14 4 2009-02-03 2
15 8 2009-02-03 3
16 1 2009-02-04 73
17 8 2009-02-04 12
18 16 2009-02-04 7
19 1 2009-02-05 53
20 8 2009-02-05 6
21 16 2009-02-05 9
22 1 2009-02-06 38
23 4 2009-02-06 6
24 8 2009-02-06 2
25 16 2009-02-06 3
26 1 2009-02-09 42
27 2 2009-02-09 2
28 4 2009-02-09 1
29 8 2009-02-09 2
30 1 2009-02-10 87
31 4 2009-02-10 2
32 8 2009-02-10 4
33 16 2009-02-10 3
34 1 2009-02-11 55
35 2 2009-02-11 6
36 4 2009-02-11 4
37 8 2009-02-11 2
38 16 2009-02-11 8
39 1 2009-02-12 153
40 2 2009-02-12 6
The plot displays the x column as the yaxis and the date as the x axis,
grouped by the tradetype column.
The timestamp column:
class(tradeflavorbyday$timestamp)
[1] "POSIXlt" "POSIXt"
So in this case I want to plot tradetype 1 (method 1):
xdates <- tradeflavorbyday$timestamp[tradeflavorbyday$tradeflavor == 1]
ydata <- tradeflavorbyday$x[tradeflavorbyday$tradeflavor == 1]
plot(xdates, ydata, col="black", xlab="Dates", ylab="Count")
Up to here it works great.
Now a abline through lm:
xylm <- lm(ydata~xdates) <------ this fails, can't do dates as below
abline(xylm, col="black")
lm(ydata~xdates)
Error in model.frame.default(formula = ydata ~ xdates,
drop.unused.levels = TRUE) :
invalid type (list) for variable 'xdates'
You might try converting timestamp as follows
xdates <- as.POSIXct(tradeflavorbyday$timestamp[tradeflavorbyday$tradeflavor == 1])
Your original code should now work.
It does, I've just tried it.
Also, regarding the op statement "(I'm sorry it's not in a runnable
form, not sure how to get that from R)":
# It's easy to read in the data
tfday <- read.table(text="
tradeflavor timestamp x
1 1 2009-01-22 1
2 2 2009-01-22 1
3 1 2009-01-23 1
[...etc...]
39 1 2009-02-12 153
40 2 2009-02-12 6
", header=TRUE, stringsAsFactors=FALSE)
# But it's better to paste the output of dput().
dput(tfday)
structure(list(tradeflavor = c(1L, 2L, 1L, 1L, 1L, 2L, 16L, 1L,
16L, 1L, 1L, 16L, 1L, 4L, 8L, 1L, 8L, 16L, 1L, 8L, 16L, 1L, 4L,
8L, 16L, 1L, 2L, 4L, 8L, 1L, 4L, 8L, 16L, 1L, 2L, 4L, 8L, 16L,
1L, 2L), timestamp = structure(c(1232582400, 1232582400, 1232668800,
1233014400, 1233100800, 1233100800, 1233100800, 1233187200, 1233187200,
1233273600, 1233532800, 1233532800, 1233619200, 1233619200, 1233619200,
1233705600, 1233705600, 1233705600, 1233792000, 1233792000, 1233792000,
1233878400, 1233878400, 1233878400, 1233878400, 1234137600, 1234137600,
1234137600, 1234137600, 1234224000, 1234224000, 1234224000, 1234224000,
1234310400, 1234310400, 1234310400, 1234310400, 1234310400, 1234396800,
1234396800), class = c("POSIXct", "POSIXt"), tzone = ""), x = c(1L,
1L, 1L, 54L, 105L, 2L, 2L, 71L, 2L, 42L, 19L, 2L, 36L, 2L, 3L,
73L, 12L, 7L, 53L, 6L, 9L, 38L, 6L, 2L, 3L, 42L, 2L, 1L, 2L,
87L, 2L, 4L, 3L, 55L, 6L, 4L, 2L, 8L, 153L, 6L)), .Names = c("tradeflavor",
"timestamp", "x"), row.names = c("1", "2", "3", "4", "5", "6",
"7", "8", "9", "10", "11", "12", "13", "14", "15", "16", "17",
"18", "19", "20", "21", "22", "23", "24", "25", "26", "27", "28",
"29", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39",
"40"), class = "data.frame")
# Now all we need to do is copy and paste this into an R session:
tfday <- structure(...etc...)
# Finally, for the sake of completeness, the rest of the code.
tfday$timestamp <- as.POSIXct(tfday$timestamp)
inx <- tfday$tradeflavor == 1 # do this once
xdates <- tfday$timestamp[inx]
ydata <- tfday$x[inx]
plot(xdates, ydata)
model <- lm(ydata ~ xdates)
abline(model)
Hope this helps,
Rui Barradas
Hope this is helpful,
Dan
Daniel J. Nordlund
Washington State Department of Social and Health Services
Planning, Performance, and Accountability
Research and Data Analysis Division
Olympia, WA 98504-5204