从特定行读取csv

Question

我从1980年开始在csv文件中有每日数据.但我只想从1985年读取数据.因为另一个文件中的其他数据集始于1985年.如何在R语言之前跳过阅读1985年以前的数据？

Answer 1

我想你想?read.csv看看所有选项.

在没有看到您的数据样本的情况下给出确切答案有点困难.

如果您的数据没有标题,并且您知道1985年数据的哪一行开始,您可以使用类似......

impordata <- read.csv(file,skip=1825)

...跳过前1825行.

否则,如果数据中有年份变量,则在导入数据后,您始终可以对数据进行子集化.

impordata <- read.csv("skiplines.csv")
impordata <- subset(impordata,year>=1985)

如果您不知道1985数据的起始位置,可以使用grep在文件的日期变量中查找1985的第一个实例,然后只保留该行的开头:

impordata <- read.csv("skiplines.csv")
impordata <- impordata[min(grep(1985,impordata$date)):nrow(impordata),]

Answer 2

以下是一些替代方案.(您可能希望之后将第一列转换为"Date"类,并可能将整个事物转换为动物园对象或其他时间序列类对象.)

# create test data
fn <- tempfile()
dd <- seq(as.Date("1980-01-01"), as.Date("1989-12-31"), by = "day")
DF <- data.frame(Date = dd, Value = seq_along(dd))
write.table(DF, file = fn, row.names = FALSE)

read.table + subset

# if file is small enough to fit in memory try this:

DF2 <- read.table(fn, header = TRUE, as.is = TRUE)
DF2 <- subset(DF2, Date >= "1985-01-01")

read.zoo

# or this which produces a zoo object and also automatically converts the 
# Date column to Date class.  Note that all columns other than the Date column
# should be numeric for it to be representable as a zoo object.
library(zoo)
z <- read.zoo(fn, header = TRUE)
zw <- window(z, start = "1985-01-01")

如果您的数据格式与示例的格式不同,则需要使用其他参数read.zoo.

多个read.table的

# if the data is very large read 1st row (DF.row1) and 1st column (DF.Date)
# and use those to set col.names= and skip=

DF.row1 <- read.table(fn, header = TRUE, nrow = 1)
nc <- ncol(DF.row1)
DF.Date <- read.table(fn, header = TRUE, as.is = TRUE, 
   colClasses = c(NA, rep("NULL", nc - 1)))
n1985 <- which.max(DF.Date$Date >= "1985-01-01")

DF3 <- read.table(fn, col.names = names(DF.row1), skip = n1985, as.is = TRUE)

sqldf

# this is probably the easiest if data set is large.

library(sqldf)
DF4 <- read.csv.sql(fn, sql = 'select * from file where Date >= "1985-01-01"')