Pattern matching using a wildcard

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If you want to examine elements inside a dataframe you should not be using ls() which only looks at the names of objects in the current workspace (or if used inside a function in the current environment). Rownames or elements inside such objects are not visible to ls() (unless of course you add an environment argument to the ls(.)-call). Try using grep() which is the workhorse function for pattern matching of character vectors:

result <- a[ grep("blue", a$x) , ]  # Note need to use `a$` to get at the `x`

If you want to use subset then consider the closely related function grepl() which returns a vector of logicals can be used in the subset argument:

subset(a, grepl("blue", a$x))
      x
2 blue1
3 blue2

Edit: Adding one “proper” use of glob2rx within subset():

result <- subset(a,  grepl(glob2rx("blue*") , x) )
result
      x
2 blue1
3 blue2

I don’t think I actually understood glob2rx until I came back to this question. (I did understand the scoping issues that were ar the root of the questioner’s difficulties. Anybody reading this should now scroll down to Gavin’s answer and upvote it.)

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