& and |
The single grep regex solutions offered to Ivan's problem were fine, but do not readily generalize to the conjunction of multiple (>2, say) regex patterns that can appear anywhere in a string and in any order. However, note that this can easily be done using the Perl zero width lookahead construction, "(?=...)" . e.g.
test <- test <- c("xyCz",
"xAyCz","xAyBzC","xCByAz","xACyB","BAyyC","CBxBAy") ## to search for strings contain "A", "B", & "C" in any order
grep("(?=.*A)(?=.*B)(?=.*C)", test, perl = TRUE)
[1] 3 4 5 6 7 Note that this matches on one or multiple instances of the patterns. If one wants only exactly one instance of each conjunct, then something like this should do:
lookfor <- c("A","B","C")
notme <- paste0("[^",lookfor,"]*")
z <- paste0("(?=", notme, lookfor, notme, "$)",collapse = "")
grep(z, test, perl = TRUE)
[1] 3 4 5 6 Cheers, Bert
On Wed, Aug 19, 2020 at 11:38 PM Ivan Calandra <calandra at rgzm.de> wrote:
Thank you all for all the very helpful answers! Best, Ivan -- Dr. Ivan Calandra TraCEr, laboratory for Traceology and Controlled Experiments MONREPOS Archaeological Research Centre and Museum for Human Behavioural Evolution Schloss Monrepos 56567 Neuwied, Germany +49 (0) 2631 9772-243 https://www.researchgate.net/profile/Ivan_Calandra On 20/08/2020 3:28, Richard O'Keefe wrote:
There are & and | operators in the R language.
There is an | operator in regular expressions.
There is NOT any & operator in regular expressions.
grep("ConfoMap&GuineaPigs", mydata, value=TRUE)
looks for elements of mydata containing the literal
string 'ConfoMap&GuineaPigs'.
foo <- c("a","b","cab","back")
foo[grepl("a",foo) & grepl("b",foo)]
[1] "cab" "back"
grepl returns a TRUE/FALSE vector.
On Thu, 20 Aug 2020 at 02:53, Ivan Calandra <calandra at rgzm.de
<mailto:calandra at rgzm.de>> wrote:
Dear useRs,
I feel really stupid, but I cannot understand why "&" doesn't work
as I
expect, while "|" does.
I have the following vector:
mydata <- c("SSFA-ConfoMap_GuineaPigs_NMPfilled.csv",
"SSFA-ConfoMap_Lithics_NMPfilled.csv",
"SSFA-ConfoMap_Sheeps_NMPfilled.csv",
"SSFA-Toothfrax_GuineaPigs.xlsx",
"SSFA-Toothfrax_Lithics.xlsx", "SSFA-Toothfrax_Sheeps.xlsx")
and I want to find the values that include both "ConfoMap" and
"GuineaPigs".
If I do:
grep("ConfoMap&GuineaPigs", mydata, value=TRUE)
it returns an empty vector, character(0).
But if I do:
grep("ConfoMap|GuineaPigs", mydata, value=TRUE)
it returns all the elements that include either "ConfoMap" or
"GuineaPigs", as I would expect.
So what is wrong with my "&" construct? How can I return the elements
that include both parts?
Thank you for your help!
Ivan
--
Dr. Ivan Calandra
TraCEr, laboratory for Traceology and Controlled Experiments
MONREPOS Archaeological Research Centre and
Museum for Human Behavioural Evolution
Schloss Monrepos
56567 Neuwied, Germany
+49 (0) 2631 9772-243
https://www.researchgate.net/profile/Ivan_Calandra
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