Eliminating 'Unprintable ASCII' characters
I think you mean the control characters: there are other unprintable characters (del for example). They are the character range [\001-\037]. E.g.
test <- intToUtf8(1:40, multiple=TRUE)
grepl("[\001-\037]", test)
[1] TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE [13] TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE [25] TRUE TRUE TRUE TRUE TRUE TRUE TRUE FALSE FALSE FALSE FALSE FALSE [37] FALSE FALSE FALSE FALSE If you want to include del, use "[\001-\037\177]". I have omitted nul (\000) which cannot occur in R character strings. You didn't give us the sessionInfo() output the posting guide asked you for, so I am presuming you are not doing this in an unusual locale: I wouldn't trust the regexp code in one of the stateful locales used for Japanese.
On Wed, 25 Nov 2009, Steven Kang wrote:
Hi all, I have a csv file containing words with *UNPRINTABLE ASCII* characters (described in the following table). Are there any viable method in eliminating these characters? I realise that *EXTENDED ASCII* characters (i.e , ?, ?, ?, ? etc) can be removed or replaced via *"gsub"* or *"gregexpr"* functions. But am not certain with the *UNPRINTABLE ASCII* characters. Your help in resolving this problem would be highly appreciated. Thanks Steven ASCII control characters (character code 0-31)The first 32 characters in the ASCII-table are unprintable control codes and are used to control peripherals such as printers. *DEC* *OCT* *HEX* *BIN* *Symbol* *HTML Number* *HTML Name* *Description* 0 000 00 00000000 NUL � Null char 1 001 01 00000001 SOH  Start of Heading 2 002 02 00000010 STX  Start of Text 3 003 03 00000011 ETX  End of Text 4 004 04 00000100 EOT  End of Transmission 5 005 05 00000101 ENQ  Enquiry 6 006 06 00000110 ACK  Acknowledgment 7 007 07 00000111 BEL  Bell 8 010 08 00001000 BS  Back Space 9 011 09 00001001 HT 	 Horizontal Tab 10 012 0A 00001010 LF 
 Line Feed 11 013 0B 00001011 VT  Vertical Tab 12 014 0C 00001100 FF  Form Feed 13 015 0D 00001101 CR 
 Carriage Return 14 016 0E 00001110 SO  Shift Out / X-On 15 017 0F 00001111 SI  Shift In / X-Off 16 020 10 00010000 DLE  Data Line Escape 17 021 11 00010001 DC1  Device Control 1 (oft. XON) 18 022 12 00010010 DC2  Device Control 2 19 023 13 00010011 DC3  Device Control 3 (oft. XOFF) 20 024 14 00010100 DC4  Device Control 4 21 025 15 00010101 NAK  Negative Acknowledgement 22 026 16 00010110 SYN  Synchronous Idle 23 027 17 00010111 ETB  End of Transmit Block 24 030 18 00011000 CAN  Cancel 25 031 19 00011001 EM  End of Medium 26 032 1A 00011010 SUB  Substitute 27 033 1B 00011011 ESC  Escape 28 034 1C 00011100 FS  File Separator 29 035 1D 00011101 GS  Group Separator 30 036 1E 00011110 RS  Record Separator 31 037 1F 00011111 US  Unit Separator [[alternative HTML version deleted]]
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595