Dear all,
I've come across a problem using strptime, can anyone explain what's
going on? I'm using version 2.7.0 on Windows XP.
Thank you
Caroline
First read in a data file using read.table
alldata = read.table(file, header=F, skip=4, colClasses =
c("character","numeric"))
dim(alldata)
[1] 223960 2
# inefficient, safe way of sorting out missing or dodgy data
alldata[,2][alldata[,2] < 0] = NA
# first ten lines of the data
alldata[1:10,]
V1 V2
1 19800604062759 NA
2 19800604062800 0.271
3 19800604111900 0.286
4 19800604134300 0.362
5 19800604144400 0.465
6 19800604163300 0.510
7 19800604175400 0.518
8 19800604185100 0.526
9 19800611110900 NA
10 19800611110959 NA
#Then convert the first column using strptime
datetimes = strptime(alldata[,1],format="%Y%m%d%H%M%S")
#Then I want to get minimum and maximum, but some seem to be missing
when they aren't.
length(as.POSIXlt(datetimes)) #also equal to length(datetimes)
[1] 9
# Why isn't this 223960? Is it something to do with the class?
# This is the really puzzling bit (to me anyway)
a =(1:223960)[is.na(datetimes)]
# which gives
1462 14295 18744 50499 50500 92472 92473 92474 92475 92476
137525 137526 137527 171066 171067 192353
# 16 values
alldata[a,]
V1 V2
1462 19810329012000 0.983
14295 19900325014300 0.219
18744 19920329014300 0.246
50499 19960331013000 0.564
50500 19960331015700 0.563
92472 19970330010200 0.173
92473 19970330011400 0.172
92474 19970330012700 0.172
92475 19970330014400 0.172
92476 19970330015500 0.172
137525 19980329011600 0.427
137526 19980329014100 0.427
137527 19980329015600 0.427
171066 19990328010300 0.223
171067 19990328011800 0.223
192353 20000326012800 0.189
datetimes[a]
[1] "1981-03-29 01:20:00" "1990-03-25 01:43:00" "1992-03-29 01:43:00"
"1996-03-31 01:30:00" "1996-03-31 01:57:00" [6] "1997-03-30 01:02:00"
"1997-03-30 01:14:00" "1997-03-30 01:27:00" "1997-03-30 01:44:00"
"1997-03-30 01:55:00" [11] "1998-03-29 01:16:00" "1998-03-29 01:41:00"
"1998-03-29 01:56:00" "1999-03-28 01:03:00" "1999-03-28 01:18:00" [16]
"2000-03-26 01:28:00"
# They're all around the end of March! I've looked at the data file and
I can't see anything funny in it around these dates.
The first few lines of the data file look like
#TZUTC+0|*|SANR08002|*|SNAMENAUL|*|SWATERDELVIN|*|CNR98808|*|
#CNAMEQ|*|CTYPEn-min-ip|*|CMW1440|*|RTIMELVLhigh-resolution|*|
#CUNITm3/s|*|RINVAL-777|*|RNR-1|*|REXCHANGE98913|*|
#RTYPEinstantaneous values|*|
19800604062759 -777.0
19800604062800 0.271
19800604111900 0.286
19800604134300 0.362
19800604144400 0.465
19800604163300 0.510
19800604175400 0.518
19800604185100 0.526
19800611110900 -777.0
19800611110959 -777.0
19800611111000 0.100
19800611211400 0.096
19800612000000 0.096
19800612065000 0.098
19800612133400 0.100
Caroline KeefJBA Consulting
South Barn, Broughton Hall, Skipton, North Yorkshire, BD23 3AE, UK
t: +44 (0)1756 799919 f: +44 (0)1756 799449
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