CODEWITHSUNDEEP
regexr
user1471980
user1471980

Reputation: 10626

how do you extract the columns that contain a certain text/string in R

I need to be able to extract columns that contain exact string that I am looking for. For example, I have this data frame x:

structure(list(Time = structure(1L, .Label = "1/1/2015", class = "factor"), 
    WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Phys.Mem.MB. = 3555L, 
    WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Phys.Mem.Free.MB. = 55L, 
    WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Swap.Free.MB. = 44L, 
    WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Cache.Free.MB. = 66L, 
    WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Swap.And.Cache.Free.MB. = 44L, 
    WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Percent.Free = 44L, 
    WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Round.Trip.Time = 44L), .Names = c("Time", 
"WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Phys.Mem.MB.", 
"WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Phys.Mem.Free.MB.", 
"WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Swap.Free.MB.", 
"WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Cache.Free.MB.", 
"WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Swap.And.Cache.Free.MB.", 
"WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Percent.Free", 
"WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Round.Trip.Time"
), class = "data.frame", row.names = c(NA, -1L))

I need to only extract the column that contains this exact match ".Total.Phys.Mem.MB."

When I do this:

x[,grepl(".Total.Phys.Mem.MB.", colnames(x)[2:ncol(x)])]

I dont get the column that contains this string in it ".Total.Phys.Mem.MB.". Is there a better way to extract the columns that contain the string in R?

Upvotes: 0

Views: 171

Answers (2)

hwnd
hwnd

Reputation: 70732

Unless fixed=TRUE is defined, grepl recognizes the pattern as a regular expression; and in regex the dot is a character of special meaning which must be escaped to match a literal.

> x[grepl("\\.Total\\.Phys\\.Mem\\.MB\\.", colnames(x))]
  WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Phys.Mem.MB.
1                                                                                    3555

OR

> x[grepl('.Total.Phys.Mem.MB.', colnames(x), fixed=TRUE)]
  WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Phys.Mem.MB.
1                                                                                    3555

Upvotes: 1

DatamineR
DatamineR

Reputation: 9618

library(dplyr)

select(x, contains(".Total.Phys.Mem.MB."))
  WTAD..Linux..Linux.Percent.of.Physical.Memory.and.Swap.Used.on.web02.Total.Phys.Mem.MB.
1                                                                                    3555

Upvotes: 1

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