There seems to be a funny interaction between lapply and "$" -- also, "$"
doesn't signal an error in some cases where "[[" does.
The $ operator accepts a string second argument in functional form:
> `$`(list(a=3,b=4),"b")
[1] 4
lapply(list(list(a=3,b=4)),function(x) `$`(x,"b"))
[[1]]
[1] 4
... but using an lapply "..." argument, this returns NULL:
> lapply(list(list(a=3,b=4)),"$","b")
[[1]]
NULL
Equally strangely, a symbol is an error in functional form:
> `$`(list(a=3,b=4),quote(`b`))
Error in list(a = 3, b = 4)$quote(b) : invalid subscript type 'language'
... but not an error in lapply, where it returns NULL:
> lapply(list(list(a=3,b=4)),`$`,quote(`b`))
[[1]]
NULL
I wonder if lapply is failing to pass the second argument to $ correctly,
since $ with various unreasonable second arguments returns NULL (shouldn't
it given an error?):
"$"(list(list(a=3,b=4)),) => NULL
lapply(list(list(a=3,b=4)),`$`,function(i)i) => NULL
Compare
"[["(list(list(a=3,b=4)),) => <<error>>
But with [[, lapply correctly gives an error:
lapply(list(list(a=3,b=4)),`[[`,function(i)i) => <<error>>
[[alternative HTML version deleted]]
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