Here is a string :
str1="ha,hihi,aaaaa,ok"
I want to get the position of "," in the str1,Which can count 3,8,14.
how can I get it in R ?
You get the desired vector using this expression:
as.integer(gregexpr(",", str1)[[1]])
The [[1]] will choose the first element of the resulting list. If str1 were a vector of a length other than 1, then gregexpr would result a list with that many items, one for each element of str1.
The as.integer will strip additional attributes, like the length of the matched text. In many situations you will be able to omit this, as other code will likely simply ignore those attributes. For output to the console it might be less confusing, though, so I included it in my answer.
Related
I have a string, and I want to extract, using regular expressions, groups of characters that are between the character : and the other character /.
typically, here is a string example I'm getting:
'abcd:45.72643,4.91203/Rou:hereanotherdata/defgh'
and so, I want to retrieved, 45.72643,4.91203 and also hereanotherdata
As they are both between characters : and /.
I tried with this syntax in a easier string where there is only 1 time the pattern,
[tt]=regexp(str,':(\w.*)/','match')
tt = ':45.72643,4.91203/'
but it works only if the pattern happens once. If I use it in string containing multiples times the pattern, I get all the string between the first : and the last /.
How can I mention that the pattern will occur multiple time, and how can I retrieve it?
Use lookaround and a lazy quantifier:
regexp(str, '(?<=:).+?(?=/)', 'match')
Example (Matlab R2016b):
>> str = 'abcd:45.72643,4.91203/Rou:hereanotherdata/defgh';
>> result = regexp(str, '(?<=:).+?(?=/)', 'match')
result =
1×2 cell array
'45.72643,4.91203' 'hereanotherdata'
In most languages this is hard to do with a single regexp. Ultimately you'll only ever get back the one string, and you want to get back multiple strings.
I've never used Matlab, so it may be possible in that language, but based on other languages, this is how I'd approach it...
I can't give you the exact code, but a search indicates that in Matlab there is a function called strsplit, example...
C = strsplit(data,':')
That should will break your original string up into an array of strings, using the ":" as the break point. You can then ignore the first array index (as it contains text before a ":"), loop the rest of the array and regexp to extract everything that comes before a "/".
So for instance...
'abcd:45.72643,4.91203/Rou:hereanotherdata/defgh'
Breaks down into an array with parts...
1 - 'abcd'
2 - '45.72643,4.91203/Rou'
3 - 'hereanotherdata/defgh'
Then Ignore 1, and extract everything before the "/" in 2 and 3.
As John Mawer and Adriaan mentioned, strsplit is a good place to start with. You can use it for both ':' and '/', but then you will not be able to determine where each of them started. If you do it with strsplit twice, you can know where the ':' starts :
A='abcd:45.72643,4.91203/Rou:hereanotherdata/defgh';
B=cellfun(#(x) strsplit(x,'/'),strsplit(A,':'),'uniformoutput',0);
Now B has cells that start with ':', and has two cells in each cell that contain '/' also. You can extract it with checking where B has more than one cell, and take the first of each of them:
C=cellfun(#(x) x{1},B(cellfun('length',B)>1),'uniformoutput',0)
C =
1×2 cell array
'45.72643,4.91203' 'hereanotherdata'
Starting in 16b you can use extractBetween:
>> str = 'abcd:45.72643,4.91203/Rou:hereanotherdata/defgh';
>> result = extractBetween(str,':','/')
result =
2×1 cell array
{'45.72643,4.91203'}
{'hereanotherdata' }
If all your text elements have the same number of delimiters this can be vectorized too.
Let's say I have a column which has values like:
foo/bar
chunky/bacon/flavor
/baz/quz/qux/bax
I.e. a variable number of strings separated by /.
In another column I want to get the last element from each of these strings, after they have been split on /. So, that column would have:
bar
flavor
bax
I can't figure this out. I can split on / and get an array, and I can see the function INDEX to get a specific numbered indexed element from the array, but can't find a way to say "the last element" in this function.
Edit:
this one is simplier:
=REGEXEXTRACT(A1,"[^/]+$")
You could use this formula:
=REGEXEXTRACT(A1,"(?:.*/)(.*)$")
And also possible to use it as ArrayFormula:
=ARRAYFORMULA(REGEXEXTRACT(A1:A3,"(?:.*/)(.*)$"))
Here's some more info:
the RegExExtract function
Some good examples of syntax
my personal list of Regex Tricks
This formula will do the same:
=INDEX(SPLIT(A1,"/"),LEN(A1)-len(SUBSTITUTE(A1,"/","")))
But it takes A1 three times, which is not prefferable.
You could do this too
=index(SPLIT(A1, "/"), COLUMNS(SPLIT(A1, "/"))-1)
Also possible, perhaps best on a copy, with Find:
.+/
(Replace with blank) and Search using regular expressions ticked.
You can try use this!
You've got the array of String, so you can acess the last element by length
String message = "chunky/bacon/flavor";
String[] outSplited = message.split("/");
System.out.println(outSplited[outSplited.length -1]);
in order to execute this code, which basically deletes a word from a sentence, we have to use split.string in order to access words.
def censor(text, word):
splitstring=text.split()
for elem in range(len(splitstring)):
if splitstring[elem]==word:
splitstring[elem]='*'*len(word)
return " ".join(splitstring)**strong text**
why can't we use use a "traditional" for-loop, as if looping through a word for a letter?
for word in text:
for elem in word:
if elem==word:
word='*'*len(word) """etc"""
There are multiple questions here:
When we iterate over a string of text, why do we get individual letters not words ?
The Zen of Python states "There should be one-- and preferably only one --obvious way to do it."
A string is a just string of characters. It may or may not have individual words in it. The most obvious way to iterate over a string is one character at a time.
When we iterate using "for word in text" and modify "word", why doesn't "text" change ?
The answer has two parts to it:
(a) Strings are immutable in Python, so whenever you modify a string, you get a new string while the original one remains unmodified. So there is no way to modify string "text" other than by reassigning "text" to a new string.
(b) Even if strings were mutable, when you iterate over an iterable, you only get copies of the elements. So modifying them has no effect on the iterable object.
"for elem in range(len(splitstring))" looks clumsy. What is the right way to do this in Python ?
Ok, I made up this question. But the answer is still important. The Pythonic way to do this is:
for elem in splitstring:
Or if you need the index of each element, then you do this:
for index, elem in enumerate(splitstring):
I have a column with these type of names:
sp_O00168_PLM_HUMAM
sp_Q8N1D5_CA158_HUMAN
sp_Q15818_NPTX1_HUMAN
tr_Q6FGH5_Q6FGH5_HUMAN
sp_Q9UJ99_CAD22_HUMAN
I want to remove everything before, and including, the second _ and everything after, and including, the third _.
I do not which to remove based on number of characters, since this is not a fixed number.
The output should be:
PLM
CA158
NPTX1
Q6FGH5
CAD22
I have played around with these, but don't quite get it right..
library(stringer)
str_sub(x,-6,-1)
That’s not really a subset in programming terminology1, it’s a substring. In order to extract partial strings, you’d usually use regular expressions (pretty much regardless of language); in R, this is accessible via sub and other related functions:
pattern = '^.*_.*_([^_]*)_.*$'
result = sub(pattern, '\\1', strings)
1 Aside: taking a subset is, as the name says, a set operation, and sets are defined by having no duplicate elements and there’s no particular order to the elements. A string by contrast is a sequence which is a very different concept.
Another possible regular expression is this:
sub("^(?:.+_){2}(.+?)_.+", "\\1", vec)
# [1] "PLM" "CA158" "NPTX1" "Q6FGH5" "CAD22"
where vec is your vector of strings.
A visual explanation:
> gsub(".*_.*_(.*)_.*", "\\1", "sp_O00168_PLM_HUMAM")
[1] "PLM"
I need to search a cell array and return a single boolean value indicating whether any cell matches a regular expression.
For example, suppose I want to find out if the cell array strs contains foo or -foo (case-insensitive). The regular expression I need to pass to regexpi is ^-?foo$.
Sample inputs:
strs={'a','b'} % result is 0
strs={'a','foo'} % result is 1
strs={'a','-FOO'} % result is 1
strs={'a','food'} % result is 0
I came up with the following solution based on How can I implement wildcard at ismember function of matlab? and Searching cell array with regex, but it seems like I should be able to simplify it:
~isempty(find(~cellfun('isempty', regexpi(strs, '^-?foo$'))))
The problem I have is that it looks rather cryptic for such a simple operation. Is there a simpler, more human-readable expression I can use to achieve the same result?
NOTE: The answer refers to the original regexp in the question: '-?foo'
You can avoid the find:
any(~cellfun('isempty', regexpi(strs, '-?foo')))
Another possibility: concatenate first all cells into a single string:
~isempty(regexpi([strs{:}], '-?foo'))
Note that you can remove the "-" sign in any of the above:
any(~cellfun('isempty', regexpi(strs, 'foo')))
~isempty(regexpi([strs{:}], 'foo'))
And that allows using strfind (with lower) instead of regexpi:
~isempty(strfind(lower([strs{:}]),'foo'))