如何修剪领先和领先空格？

Question

I am having some troubles with leading and trailing whitespace in a data.frame. Eg I like to take a look at a specific row in a data.frame based on a certain condition:

> myDummy[myDummy$country == c("Austria"),c(1,2,3:7,19)] 

[1] codeHelper     country        dummyLI    dummyLMI       dummyUMI       
[6] dummyHInonOECD dummyHIOECD    dummyOECD      
<0 rows> (or 0-length row.names)

I was wondering why I didn't get the expected output since the country Austria obviously existed in my data.frame. After looking through my code history and trying to figure out what went wrong I tried:

> myDummy[myDummy$country == c("Austria "),c(1,2,3:7,19)]
   codeHelper  country dummyLI dummyLMI dummyUMI dummyHInonOECD dummyHIOECD
18        AUT Austria        0        0        0              0           1
   dummyOECD
18         1

All I have changed in the command is an additional whitespace after Austria.

Further annoying problems obviously arise. Eg when I like to merge two frames based on the country column. One data.frame uses "Austria " while the other frame has "Austria". The matching doesn't work.

1. Is there a nice way to 'show' the whitespace on my screen so that i am aware of the problem?
2. And can I remove the leading and trailing whitespace in R?

So far I used to write a simple Perl script which removes the whitespace but it would be nice if I can somehow do it inside R.

转载于:https://stackoverflow.com/questions/2261079/how-to-trim-leading-and-trailing-whitespace

Answer 1

Probably the best way is to handle the trailing whitespaces when you read your data file. If you use read.csv or read.table you can set the parameterstrip.white=TRUE.

If you want to clean strings afterwards you could use one of these functions:

# returns string w/o leading whitespace
trim.leading <- function (x)  sub("^\\s+", "", x)

# returns string w/o trailing whitespace
trim.trailing <- function (x) sub("\\s+$", "", x)

# returns string w/o leading or trailing whitespace
trim <- function (x) gsub("^\\s+|\\s+$", "", x)

To use one of these functions on myDummy$country:

 myDummy$country <- trim(myDummy$country)

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To 'show' the whitespace you could use:

 paste(myDummy$country)

which will show you the strings surrounded by quotation marks (") making whitespaces easier to spot.