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R 的 data.table 資料操作
Matt Dowle, Arun Srinivasan
Instructors, DataCamp
用 integer64 讀取大整數
- R 預設只能表示小於等於 2^31 - 1 = 2147483647 的數字。
- 大整數會自動讀成
bit64套件提供的integer64型別。
ans <- fread("id,name\n1234567890123,Jane\n5284782381811,John\n")
ans
id name
1234567890123 Jane
5284782381811 John
class(ans$id)
"integer64"
用 colClasses 指定欄位型別
str <- "x1,x2,x3,x4,x5\n1,2,1.5,true,cc\n3,4,2.5,false,ff"ans <- fread(str, colClasses = c(x5 = "factor")) str(ans)
Classes 'data.table' and 'data.frame': 2 obs. of 5 variables:
$ x1: int 1 3
$ x2: int 2 4
$ x3: num 1.5 2.5
$ x4: logi TRUE FALSE
$ x5: Factor w/ 2 levels "cc","ff": 1 2
用 colClasses 指定欄位型別
ans <- fread(str, colClasses = c("integer", "integer",
"numeric", "logical", "factor"))
str(ans)
Classes 'data.table' and 'data.frame': 2 obs. of 5 variables:
$ x1: int 1 3
$ x2: int 2 4
$ x3: num 1.5 2.5
$ x4: logi TRUE FALSE
$ x5: Factor w/ 2 levels "cc","ff": 1 2
用 colClasses 指定欄位型別
str <- "x1,x2,x3,x4,x5,x6\n1,2,1.5,2.5,aa,bb\n3,4,5.5,6.5,cc,dd"
ans <- fread(str, colClasses = list(numeric = 1:4, factor = c("x5", "x6")))
str(ans)
Classes 'data.table' and 'data.frame': 2 obs. of 6 variables:
$ x1: num 1 3
$ x2: num 2 4
$ x3: num 1.5 5.5
$ x4: num 2.5 6.5
$ x5: Factor w/ 2 levels "aa","cc": 1 2
$ x6: Factor w/ 2 levels "bb","dd": 1 2
參數 fill
str <- "1,2\n3,4,a\n5,6\n7,8,b"
fread(str)
V1 5 6
7 8 b
Warning message:
In fread(str) :
Detected 2 column names but the data has 3 columns (i.e. invalid file).
Added 1 extra default column name for the first column which is guessed to
be row names or an index.
Use setnames() afterwards if this guess is not correct,
or fix the file write command that created the file to create a valid file.
參數 fill
fread(str, fill = TRUE)
V1 V2 V3
1 2
3 4 a
5 6
7 8 b
參數 na.strings
遺漏值常被編碼為："999"、"##NA"、"N/A"。
str <- "x,y,z\n1,###,3\n2,4,###\n#N/A,7,9"
ans <- fread(str, na.strings = c("###", "#N/A"))
ans
x y z
1 NA 3
2 4 NA
NA 7 9
一起來練習吧！
R 的 data.table 資料操作
