仅读取选定的列 [英] Only read selected columns
问题描述
有人可以告诉我如何例如通过使用read.table()
来读取以下数据每年的前6个月(7列)吗?
Can anyone please tell me how to read only the first 6 months (7 columns) for each year of the data below, for example by using read.table()
?
Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
2009 -41 -27 -25 -31 -31 -39 -25 -15 -30 -27 -21 -25
2010 -41 -27 -25 -31 -31 -39 -25 -15 -30 -27 -21 -25
2011 -21 -27 -2 -6 -10 -32 -13 -12 -27 -30 -38 -29
推荐答案
说数据在文件data.txt
中,则可以使用read.table()
的colClasses
参数跳过列.这里前7列中的数据为"integer"
,我们将其余6列设置为"NULL"
,表示应跳过
Say the data are in file data.txt
, you can use the colClasses
argument of read.table()
to skip columns. Here the data in the first 7 columns are "integer"
and we set the remaining 6 columns to "NULL"
indicating they should be skipped
> read.table("data.txt", colClasses = c(rep("integer", 7), rep("NULL", 6)),
+ header = TRUE)
Year Jan Feb Mar Apr May Jun
1 2009 -41 -27 -25 -31 -31 -39
2 2010 -41 -27 -25 -31 -31 -39
3 2011 -21 -27 -2 -6 -10 -32
根据实际数据类型,将"integer"
更改为?read.table
中详细说明的可接受的类型之一.
Change "integer"
to one of the accepted types as detailed in ?read.table
depending on the real type of data.
data.txt
看起来像这样:
$ cat data.txt
"Year" "Jan" "Feb" "Mar" "Apr" "May" "Jun" "Jul" "Aug" "Sep" "Oct" "Nov" "Dec"
2009 -41 -27 -25 -31 -31 -39 -25 -15 -30 -27 -21 -25
2010 -41 -27 -25 -31 -31 -39 -25 -15 -30 -27 -21 -25
2011 -21 -27 -2 -6 -10 -32 -13 -12 -27 -30 -38 -29
并且是通过使用
write.table(dat, file = "data.txt", row.names = FALSE)
其中dat
是
dat <- structure(list(Year = 2009:2011, Jan = c(-41L, -41L, -21L), Feb = c(-27L,
-27L, -27L), Mar = c(-25L, -25L, -2L), Apr = c(-31L, -31L, -6L
), May = c(-31L, -31L, -10L), Jun = c(-39L, -39L, -32L), Jul = c(-25L,
-25L, -13L), Aug = c(-15L, -15L, -12L), Sep = c(-30L, -30L, -27L
), Oct = c(-27L, -27L, -30L), Nov = c(-21L, -21L, -38L), Dec = c(-25L,
-25L, -29L)), .Names = c("Year", "Jan", "Feb", "Mar", "Apr",
"May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"), class = "data.frame",
row.names = c(NA, -3L))
如果事先不知道列数,则实用程序功能count.fields
将读取文件并计算每行中的字段数.
If the number of columns is not known beforehand, the utility function count.fields
will read through the file and count the number of fields in each line.
## returns a vector equal to the number of lines in the file
count.fields("data.txt", sep = "\t")
## returns the maximum to set colClasses
max(count.fields("data.txt", sep = "\t"))
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