fread中的空白未被识别为NA [英] Blank space not recognised as NA in fread

问题描述

我有一个大文件，必须在R中导入。为此，我使用了 fread 。 fread 会将数字字段中的空格识别为NA，但无法将字符和integer64字段中的空格识别为NA。

I have a large file which has to be imported in R. I used fread for this purpose. fread is recognizing blank spaces from numeric fields as NA but it is not recognizing blank spaces from character and integer64 fields as NA.

read 将空格识别为字符字段的空单元格，并将空格识别为0的integer64字段。

fread recognises blank space as an empty cell for character fields and it recognises blank space as 0 for integer64 fields.

当我使用 read.table 导入相同的数据时，它会将所有空格识别为NA。

When I imported the same data using read.table, it recognizes all blank spaces as NA.

请找到可复制的示例，

library(data.table)
x1 <- c("","","")
x2 <- c("1006678566","","1011160152")
x3 <- c("","ac","")
x4 <- c("","2","3")
df <- cbind.data.frame(x1,x2,x3,x4)
write.csv(df,"tr.csv")

tr1 <- fread("tr.csv", header=T, fill = T,
             sep= ",", na.strings = c("",NA), data.table = F,
             stringsAsFactors = FALSE)

tr2 <- read.table("tr.csv", fill = TRUE, header=T, 
                  sep= ",", na.strings = c(""," ", NA), 
                  stringsAsFactors = FALSE)

详细输出：

Input contains no \n. Taking this to be a filename to open
[01] Check arguments
  Using 4 threads (omp_get_max_threads()=4, nth=4)
  NAstrings = [<<>>, <<NA>>]
  None of the NAstrings look like numbers.
  show progress = 1
  0/1 column will be read as integer
[02] Opening the file
  Opening file tr.csv
  File opened, size = 409 bytes.
  Memory mapped ok
[03] Detect and skip BOM
[04] Arrange mmap to be \0 terminated
  \n has been found in the input and different lines can end with different line endings (e.g. mixed \n and \r\n in one file). This is common and ideal.
[05] Skipping initial rows if needed
  Positioned on line 1 starting: <<"","x1","x2","x3","x4","x5","x>>
[06] Detect separator, quoting rule, and ncolumns
  Using supplied sep ','
  sep=','  with 7 fields using quote rule 0
  Detected 7 columns on line 1. This line is either column names or first data row. Line starts as: <<"","x1","x2","x3","x4","x5","x>>
  Quote rule picked = 0
  fill=true and the most number of columns found is 7
[07] Detect column types, good nrow estimate and whether first row is column names
  'header' changed by user from 'auto' to true
  Number of sampling jump points = 1 because (407 bytes from row 1 to eof) / (2 * 407 jump0size) == 0
  Type codes (jump 000)    : 56A255A  Quote rule 0
  All rows were sampled since file is small so we know nrow=16 exactly
[08] Assign column names
[09] Apply user overrides on column types
  After 0 type and 0 drop user overrides : 56A255A
[10] Allocate memory for the datatable
  Allocating 7 column slots (7 - 0 dropped) with 16 rows
[11] Read the data
  jumps=[0..1), chunk_size=1048576, total_size=373
Read 16 rows x 7 columns from 409 bytes file in 00:00.042 wall clock time
[12] Finalizing the datatable
  Type counts:
         1 : bool8     '2'
         3 : int32     '5'
         1 : int64     '6'
         2 : string    'A'
=============================
   0.009s ( 22%) Memory map 0.000GB file
   0.029s ( 68%) sep=',' ncol=7 and header detection
   0.002s (  5%) Column type detection using 16 sample rows
   0.001s (  2%) Allocation of 16 rows x 7 cols (0.000GB) of which 16 (100%) rows used
   0.001s (  2%) Reading 1 chunks (0 swept) of 1.000MB (each chunk 16 rows) using 1 threads
   +    0.000s (  0%) Parse to row-major thread buffers (grown 0 times)
   +    0.000s (  0%) Transpose
   +    0.001s (  2%) Waiting
   0.000s (  0%) Rereading 0 columns due to out-of-sample type exceptions
   0.042s        Total

请帮助我解决这个问题。

Please help me solve this issue.

谢谢！

推荐答案

在读取文件后，如果要避免其他操作，可以尝试使用

In case you want to avoid the additional manipulation after reading the file, you could try using

quote = FALSE

写入c时sv。这样可以防止使用引号。 " 周围的值和所有缺少的值现在应读为 NA s。看起来应该像这样-

when writing to csv. This prevents the use of quotations " " around the values and all missing values should now be read as NAs. It should look like this -

# also turned off row names to prevent an additional column when reading the file.
write.csv(df, "tr.csv", quote = FALSE, row.names = FALSE) 

< h3>输出-

tr1 <- fread("tr.csv", header=T, fill = T,
             sep= ",", na.strings = c("",NA), data.table = F,
             stringsAsFactors = FALSE)
tr1

 x1         x2   x3 x4
1 NA 1006678566 <NA> NA
2 NA         NA   ac  2
3 NA 1011160152 <NA>  3

tr2 <- read.table("tr.csv", fill = TRUE, header=T, 
                  sep= ",", na.strings = c(""," ", NA), 
                  stringsAsFactors = FALSE)
tr2

  x1         x2   x3 x4
1 NA 1006678566 <NA> NA
2 NA         NA   ac  2
3 NA 1011160152 <NA>  3

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