as.date在数据集中创建一些NA [英] as.date creates some NAs in dataset
问题描述
我有一个简单的小数据集:
I have a simple little dataset:
> str(SFdischg)
'data.frame': 11932 obs. of 4 variables:
$ date: Factor w/ 11932 levels "1/01/1985","1/01/1986",..: 97 4409 8697 9677 10069 10461 10853 11245 11637 489 ...
$ ddmm: Factor w/ 366 levels "01-Apr","01-Aug",..: 1 13 25 37 49 61 73 85 97 109 ...
$ year: int 1984 1984 1984 1984 1984 1984 1984 1984 1984 1984 ...
$ cfs : int 1500 1430 1500 1850 1810 1830 1850 1880 1970 1980 ...
我希望有一列日期,以便可以绘制时间数据:
I would like to have a column of dates so that I can plot temporal data:
SFdischg$daymo <- as.Date(SFdischg$ddmm, format="%d-%b")
> summary(SFdischg)
date ddmm year cfs daymo
1/01/1985: 1 01-Apr : 33 Min. :1984 Min. : 172 Min. :2018-01-01
1/01/1986: 1 01-Aug : 33 1st Qu.:1992 1st Qu.: 705 1st Qu.:2018-04-04
1/01/1987: 1 01-Jul : 33 Median :2000 Median : 948 Median :2018-07-03
1/01/1988: 1 01-Jun : 33 Mean :2000 Mean :1374 Mean :2018-07-02
1/01/1989: 1 01-May : 33 3rd Qu.:2008 3rd Qu.:1340 3rd Qu.:2018-10-01
1/01/1990: 1 01-Nov : 33 Max. :2016 Max. :8100 Max. :2018-12-31
(Other) :11926 (Other):11734 NA's :8
但是,daymo
现在有8个NA,我不知道为什么(这使绘制变得困难!).当ddmm
中没有缺失数据时,少数NA来自何处?我该如何避免它们?我缺少明显的东西吗?
However, daymo
now has 8 NAs and I can't understand why (and it makes it difficult to plot!). Where does the handful of NAs come from when there is no missing data in ddmm
? How can I avoid them? Am I missing something obvious?
推荐答案
我的猜测是,您在ddmm
列中拥有的某些因子数据无法正确解析为日期.您可以使用以下方法揭示这些错误的值:
My guess is that some of the factor data you have in the ddmm
column cannot be parsed correctly into a date. You may reveal these bad values using:
SFdischg$ddmm[is.na(as.Date(SFdischg$ddmm, format="%d-%b"))]
请注意,由于ddmm
列中没有年份组成部分,因此R似乎会自动将当前年份2018分配给该日期.理想情况下,您应该使用包含一年的来源信息来建立日期.
Note that since there is no year component in the ddmm
column, R appears to be automatically assigning the current year 2018 to the date. Ideally, you should be building your date using source information which includes a year.
编辑:根据您在下面的评论,有问题的行的日期为19-Feb
.这意味着这些日期甚至可能都不是从2018年开始的,这不是not年,而其2月只有28天.这说明了在解析日期(包括年份)时使用全套信息的重要性.
Based on your comment below, the offending rows had 19-Feb
as the date. This implies that these dates were perhaps not even from 2018, which was not a leap year, and whose February had only 28 days. This illustrates the importance of working with a full set of information when parsing the date, including the year.
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