Obtaining names of data frame in Julia

Question

I am trying to simply extract the list of names of a dataframe columns in Julia, but I get this error message:

ERROR: MethodError: objects of type Array{String,1} are not callable
Use square brackets [] for indexing an Array.

I am simply doing a call names(df).

(It also complains about some IOerror). Thanks.

---

Edit: Here is the (ridiculously long) error I get with the MWE suggested below:

julia> df = DataFrame(:a => [2,3,5])
3×1 DataFrame
¦ Row ¦ a     ¦
¦     ¦ Int64 ¦
+-----+-------¦
¦ 1   ¦ 2     ¦
¦ 2   ¦ 3     ¦
¦ 3   ¦ 5     ¦

julia> names(df)
ERROR: MethodError: objects of type Array{String,1} are not callable
Use square brackets [] for indexing an Array.
Stacktrace:
 [1] top-level scope at REPL[144]:1
caused by [exception 6]
IOError: symlink: operation not permitted (EPERM)
Stacktrace:
 [1] uv_error at .\libuv.jl:97 [inlined]
 [2] symlink(::String, ::String) at .\file.jl:851
 [3] probe_symlink_creation(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\PlatformEngines.jl:131
 [4] #unpack#95(::Bool, ::typeof(Pkg.PlatformEngines.unpack), ::String, ::String) at D:\buildbot\wo
rker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:727
 [5] #unpack at .\logging.jl:0 [inlined]
 [6] #download_verify_unpack#100(::Nothing, ::Bool, ::Bool, ::Bool, ::typeof(Pkg.PlatformEngines.do
wnload_verify_unpack), ::String, ::String, ::String) at D:\buildbot\worker\package_win64\build\usr\
share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:894
 [7] #download_verify_unpack at .\none:0 [inlined]
 [8] #download_artifact#38(::Bool, ::typeof(Pkg.Artifacts.download_artifact), ::Base.SHA1, ::String
, ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts
.jl:744
 [9] #download_artifact at .\none:0 [inlined]
 [10] #ensure_artifact_installed#42(::Pkg.BinaryPlatforms.Platform, ::Bool, ::typeof(Pkg.Artifacts.
ensure_artifact_installed), ::String, ::Dict{String,Any}, ::String) at D:\buildbot\worker\package_w
in64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:869
 [11] (::Pkg.Artifacts.var"#kw##ensure_artifact_installed")(::NamedTuple{(:platform, :verbose),Tupl
e{Pkg.BinaryPlatforms.Windows,Bool}}, ::typeof(Pkg.Artifacts.ensure_artifact_installed), ::String,
::Dict{String,Any}, ::String) at .\none:0
 [12] #ensure_all_artifacts_installed#43(::Pkg.BinaryPlatforms.Platform, ::Nothing, ::Bool, ::Bool,
 ::typeof(Pkg.Artifacts.ensure_all_artifacts_installed), ::String) at D:\buildbot\worker\package_wi
n64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:919
 [13] #ensure_all_artifacts_installed at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\Operations.jl:0 [inlined]
 [14] #download_artifacts#78(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{String,1}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v
1.3\Pkg\src\Operations.jl:580
 [15] #download_artifacts at .\none:0 [inlined]
 [16] #download_artifacts#73(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win64\build\usr\share
\julia\stdlib\v1.3\Pkg\src\Operations.jl:570
 [17] (::Pkg.Operations.var"#kw##download_artifacts")(::NamedTuple{(:platform,),Tuple{Pkg.BinaryPla
tforms.Windows}}, ::typeof(Pkg.Operations.download_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at
 .\none:0
 [18] #add#112(::Bool, ::Pkg.BinaryPlatforms.Windows, ::typeof(Pkg.Operations.add), ::Pkg.Types.Con
text, ::Array{Pkg.Types.PackageSpec,1}, ::Array{Base.UUID,1}) at D:\buildbot\worker\package_win64\b
uild\usr\share\julia\stdlib\v1.3\Pkg\src\Operations.jl:1017
 [19] #add at .\none:0 [inlined]
 [20] #add#25(::Bool, ::Pkg.BinaryPlatforms.Windows, ::Base.Iterators.Pairs{Union{},Union{},Tuple{}
,NamedTuple{,Tuple{}}}, ::typeof(Pkg.API.add), ::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1
}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:102
 [21] add(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win6
4\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:72
 [22] #add#24 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
69 [inlined]
 [23] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:69 [
inlined]
 [24] #add#21 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
67 [inlined]
 [25] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:67 [
inlined]
 [26] #add#20(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{,Tuple{}}}, ::typeof(Pkg.AP
I.add), ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API
.jl:66
 [27] add(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\A
PI.jl:66
 [28] top-level scope at REPL[65]:1
caused by [exception 5]
IOError: symlink: operation not permitted (EPERM)
Stacktrace:
 [1] uv_error at .\libuv.jl:97 [inlined]
 [2] symlink(::String, ::String) at .\file.jl:851
 [3] probe_symlink_creation(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\PlatformEngines.jl:131
 [4] #unpack#95(::Bool, ::typeof(Pkg.PlatformEngines.unpack), ::String, ::String) at D:\buildbot\wo
rker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:727
 [5] #unpack at .\logging.jl:0 [inlined]
 [6] #download_verify_unpack#100(::Nothing, ::Bool, ::Bool, ::Bool, ::typeof(Pkg.PlatformEngines.do
wnload_verify_unpack), ::String, ::String, ::String) at D:\buildbot\worker\package_win64\build\usr\
share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:894
 [7] #download_verify_unpack at .\none:0 [inlined]
 [8] #download_artifact#38(::Bool, ::typeof(Pkg.Artifacts.download_artifact), ::Base.SHA1, ::String
, ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts
.jl:744
 [9] #download_artifact at .\none:0 [inlined]
 [10] #ensure_artifact_installed#42(::Pkg.BinaryPlatforms.Platform, ::Bool, ::typeof(Pkg.Artifacts.
ensure_artifact_installed), ::String, ::Dict{String,Any}, ::String) at D:\buildbot\worker\package_w
in64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:869
 [11] (::Pkg.Artifacts.var"#kw##ensure_artifact_installed")(::NamedTuple{(:platform, :verbose),Tupl
e{Pkg.BinaryPlatforms.Windows,Bool}}, ::typeof(Pkg.Artifacts.ensure_artifact_installed), ::String,
::Dict{String,Any}, ::String) at .\none:0
 [12] #ensure_all_artifacts_installed#43(::Pkg.BinaryPlatforms.Platform, ::Nothing, ::Bool, ::Bool,
 ::typeof(Pkg.Artifacts.ensure_all_artifacts_installed), ::String) at D:\buildbot\worker\package_wi
n64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:919
 [13] #ensure_all_artifacts_installed at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\Operations.jl:0 [inlined]
 [14] #download_artifacts#78(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{String,1}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v
1.3\Pkg\src\Operations.jl:580
 [15] #download_artifacts at .\none:0 [inlined]
 [16] #download_artifacts#73(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win64\build\usr\share
\julia\stdlib\v1.3\Pkg\src\Operations.jl:570
 [17] (::Pkg.Operations.var"#kw##download_artifacts")(::NamedTuple{(:platform,),Tuple{Pkg.BinaryPla
tforms.Windows}}, ::typeof(Pkg.Operations.download_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at
 .\none:0
 [18] #add#112(::Bool, ::Pkg.BinaryPlatforms.Windows, ::typeof(Pkg.Operations.add), ::Pkg.Types.Con
text, ::Array{Pkg.Types.PackageSpec,1}, ::Array{Base.UUID,1}) at D:\buildbot\worker\package_win64\b
uild\usr\share\julia\stdlib\v1.3\Pkg\src\Operations.jl:1017
 [19] #add at .\none:0 [inlined]
 [20] #add#25(::Bool, ::Pkg.BinaryPlatforms.Windows, ::Base.Iterators.Pairs{Union{},Union{},Tuple{}
,NamedTuple{,Tuple{}}}, ::typeof(Pkg.API.add), ::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1
}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:102
 [21] add(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win6
4\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:72
 [22] #add#24 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
69 [inlined]
 [23] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:69 [
inlined]
 [24] #add#21 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
67 [inlined]
 [25] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:67 [
inlined]
 [26] #add#20(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{,Tuple{}}}, ::typeof(Pkg.AP
I.add), ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API
.jl:66
 [27] add(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\A
PI.jl:66
 [28] top-level scope at REPL[65]:1
caused by [exception 4]
IOError: symlink: operation not permitted (EPERM)
Stacktrace:
 [1] uv_error at .\libuv.jl:97 [inlined]
 [2] symlink(::String, ::String) at .\file.jl:851
 [3] probe_symlink_creation(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\PlatformEngines.jl:131
 [4] #unpack#95(::Bool, ::typeof(Pkg.PlatformEngines.unpack), ::String, ::String) at D:\buildbot\wo
rker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:727
 [5] #unpack at .\logging.jl:0 [inlined]
 [6] #download_verify_unpack#100(::Nothing, ::Bool, ::Bool, ::Bool, ::typeof(Pkg.PlatformEngines.do
wnload_verify_unpack), ::String, ::String, ::String) at D:\buildbot\worker\package_win64\build\usr\
share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:894
 [7] #download_verify_unpack at .\none:0 [inlined]
 [8] #download_artifact#38(::Bool, ::typeof(Pkg.Artifacts.download_artifact), ::Base.SHA1, ::String
, ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts
.jl:744
 [9] #download_artifact at .\none:0 [inlined]
 [10] #ensure_artifact_installed#42(::Pkg.BinaryPlatforms.Platform, ::Bool, ::typeof(Pkg.Artifacts.
ensure_artifact_installed), ::String, ::Dict{String,Any}, ::String) at D:\buildbot\worker\package_w
in64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:869
 [11] (::Pkg.Artifacts.var"#kw##ensure_artifact_installed")(::NamedTuple{(:platform, :verbose),Tupl
e{Pkg.BinaryPlatforms.Windows,Bool}}, ::typeof(Pkg.Artifacts.ensure_artifact_installed), ::String,
::Dict{String,Any}, ::String) at .\none:0
 [12] #ensure_all_artifacts_installed#43(::Pkg.BinaryPlatforms.Platform, ::Nothing, ::Bool, ::Bool,
 ::typeof(Pkg.Artifacts.ensure_all_artifacts_installed), ::String) at D:\buildbot\worker\package_wi
n64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:919
 [13] #ensure_all_artifacts_installed at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\Operations.jl:0 [inlined]
 [14] #download_artifacts#78(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{String,1}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v
1.3\Pkg\src\Operations.jl:580
 [15] #download_artifacts at .\none:0 [inlined]
 [16] #download_artifacts#73(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win64\build\usr\share
\julia\stdlib\v1.3\Pkg\src\Operations.jl:570
 [17] (::Pkg.Operations.var"#kw##download_artifacts")(::NamedTuple{(:platform,),Tuple{Pkg.BinaryPla
tforms.Windows}}, ::typeof(Pkg.Operations.download_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at
 .\none:0
 [18] #add#112(::Bool, ::Pkg.BinaryPlatforms.Windows, ::typeof(Pkg.Operations.add), ::Pkg.Types.Con
text, ::Array{Pkg.Types.PackageSpec,1}, ::Array{Base.UUID,1}) at D:\buildbot\worker\package_win64\b
uild\usr\share\julia\stdlib\v1.3\Pkg\src\Operations.jl:1017
 [19] #add at .\none:0 [inlined]
 [20] #add#25(::Bool, ::Pkg.BinaryPlatforms.Windows, ::Base.Iterators.Pairs{Union{},Union{},Tuple{}
,NamedTuple{,Tuple{}}}, ::typeof(Pkg.API.add), ::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1
}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:102
 [21] add(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win6
4\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:72
 [22] #add#24 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
69 [inlined]
 [23] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:69 [
inlined]
 [24] #add#21 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
67 [inlined]
 [25] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:67 [
inlined]
 [26] #add#20(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{,Tuple{}}}, ::typeof(Pkg.AP
I.add), ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API
.jl:66
 [27] add(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\A
PI.jl:66
 [28] top-level scope at REPL[65]:1
caused by [exception 3]
IOError: symlink: operation not permitted (EPERM)
Stacktrace:
 [1] uv_error at .\libuv.jl:97 [inlined]
 [2] symlink(::String, ::String) at .\file.jl:851
 [3] probe_symlink_creation(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\PlatformEngines.jl:131
 [4] #unpack#95(::Bool, ::typeof(Pkg.PlatformEngines.unpack), ::String, ::String) at D:\buildbot\wo
rker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:727
 [5] #unpack at .\logging.jl:0 [inlined]
 [6] #download_verify_unpack#100(::Nothing, ::Bool, ::Bool, ::Bool, ::typeof(Pkg.PlatformEngines.do
wnload_verify_unpack), ::String, ::String, ::String) at D:\buildbot\worker\package_win64\build\usr\
share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:894
 [7] #download_verify_unpack at .\none:0 [inlined]
 [8] #download_artifact#38(::Bool, ::typeof(Pkg.Artifacts.download_artifact), ::Base.SHA1, ::String
, ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts
.jl:744
 [9] #download_artifact at .\none:0 [inlined]
 [10] #ensure_artifact_installed#42(::Pkg.BinaryPlatforms.Platform, ::Bool, ::typeof(Pkg.Artifacts.
ensure_artifact_installed), ::String, ::Dict{String,Any}, ::String) at D:\buildbot\worker\package_w
in64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:869
 [11] (::Pkg.Artifacts.var"#kw##ensure_artifact_installed")(::NamedTuple{(:platform, :verbose),Tupl
e{Pkg.BinaryPlatforms.Windows,Bool}}, ::typeof(Pkg.Artifacts.ensure_artifact_installed), ::String,
::Dict{String,Any}, ::String) at .\none:0
 [12] #ensure_all_artifacts_installed#43(::Pkg.BinaryPlatforms.Platform, ::Nothing, ::Bool, ::Bool,
 ::typeof(Pkg.Artifacts.ensure_all_artifacts_installed), ::String) at D:\buildbot\worker\package_wi
n64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:919
 [13] #ensure_all_artifacts_installed at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\Operations.jl:0 [inlined]
 [14] #download_artifacts#78(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{String,1}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v
1.3\Pkg\src\Operations.jl:580
 [15] #download_artifacts at .\none:0 [inlined]
 [16] #download_artifacts#73(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win64\build\usr\share
\julia\stdlib\v1.3\Pkg\src\Operations.jl:570
 [17] (::Pkg.Operations.var"#kw##download_artifacts")(::NamedTuple{(:platform,),Tuple{Pkg.BinaryPla
tforms.Windows}}, ::typeof(Pkg.Operations.download_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at
 .\none:0
 [18] #add#112(::Bool, ::Pkg.BinaryPlatforms.Windows, ::typeof(Pkg.Operations.add), ::Pkg.Types.Con
text, ::Array{Pkg.Types.PackageSpec,1}, ::Array{Base.UUID,1}) at D:\buildbot\worker\package_win64\b
uild\usr\share\julia\stdlib\v1.3\Pkg\src\Operations.jl:1017
 [19] #add at .\none:0 [inlined]
 [20] #add#25(::Bool, ::Pkg.BinaryPlatforms.Windows, ::Base.Iterators.Pairs{Union{},Union{},Tuple{}
,NamedTuple{,Tuple{}}}, ::typeof(Pkg.API.add), ::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1
}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:102
 [21] add(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win6
4\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:72
 [22] #add#24 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
69 [inlined]
 [23] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:69 [
inlined]
 [24] #add#21 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
67 [inlined]
 [25] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:67 [
inlined]
 [26] #add#20(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{,Tuple{}}}, ::typeof(Pkg.AP
I.add), ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API
.jl:66
 [27] add(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\A
PI.jl:66
 [28] top-level scope at REPL[20]:1
caused by [exception 2]
IOError: symlink: operation not permitted (EPERM)
Stacktrace:
 [1] uv_error at .\libuv.jl:97 [inlined]
 [2] symlink(::String, ::String) at .\file.jl:851
 [3] probe_symlink_creation(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\PlatformEngines.jl:131
 [4] #unpack#95(::Bool, ::typeof(Pkg.PlatformEngines.unpack), ::String, ::String) at D:\buildbot\wo
rker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:727
 [5] #unpack at .\logging.jl:0 [inlined]
 [6] #download_verify_unpack#100(::Nothing, ::Bool, ::Bool, ::Bool, ::typeof(Pkg.PlatformEngines.do
wnload_verify_unpack), ::String, ::String, ::String) at D:\buildbot\worker\package_win64\build\usr\
share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:894
 [7] #download_verify_unpack at .\none:0 [inlined]
 [8] #download_artifact#38(::Bool, ::typeof(Pkg.Artifacts.download_artifact), ::Base.SHA1, ::String
, ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts
.jl:744
 [9] #download_artifact at .\none:0 [inlined]
 [10] #ensure_artifact_installed#42(::Pkg.BinaryPlatforms.Platform, ::Bool, ::typeof(Pkg.Artifacts.
ensure_artifact_installed), ::String, ::Dict{String,Any}, ::String) at D:\buildbot\worker\package_w
in64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:869
 [11] (::Pkg.Artifacts.var"#kw##ensure_artifact_installed")(::NamedTuple{(:platform, :verbose),Tupl
e{Pkg.BinaryPlatforms.Windows,Bool}}, ::typeof(Pkg.Artifacts.ensure_artifact_installed), ::String,
::Dict{String,Any}, ::String) at .\none:0
 [12] #ensure_all_artifacts_installed#43(::Pkg.BinaryPlatforms.Platform, ::Nothing, ::Bool, ::Bool,
 ::typeof(Pkg.Artifacts.ensure_all_artifacts_installed), ::String) at D:\buildbot\worker\package_wi
n64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:919
 [13] #ensure_all_artifacts_installed at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\Operations.jl:0 [inlined]
 [14] #download_artifacts#78(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{String,1}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v
1.3\Pkg\src\Operations.jl:580
 [15] #download_artifacts at .\none:0 [inlined]
 [16] #download_artifacts#73(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win64\build\usr\share
\julia\stdlib\v1.3\Pkg\src\Operations.jl:570
 [17] (::Pkg.Operations.var"#kw##download_artifacts")(::NamedTuple{(:platform,),Tuple{Pkg.BinaryPla
tforms.Windows}}, ::typeof(Pkg.Operations.download_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at
 .\none:0
 [18] #add#112(::Bool, ::Pkg.BinaryPlatforms.Windows, ::typeof(Pkg.Operations.add), ::Pkg.Types.Con
text, ::Array{Pkg.Types.PackageSpec,1}, ::Array{Base.UUID,1}) at D:\buildbot\worker\package_win64\b
uild\usr\share\julia\stdlib\v1.3\Pkg\src\Operations.jl:1017
 [19] #add at .\none:0 [inlined]
 [20] #add#25(::Bool, ::Pkg.BinaryPlatforms.Windows, ::Base.Iterators.Pairs{Union{},Union{},Tuple{}
,NamedTuple{,Tuple{}}}, ::typeof(Pkg.API.add), ::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1
}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:102
 [21] add(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win6
4\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:72
 [22] #add#24 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
69 [inlined]
 [23] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:69 [
inlined]
 [24] #add#21 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
67 [inlined]
 [25] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:67 [
inlined]
 [26] #add#20(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{,Tuple{}}}, ::typeof(Pkg.AP
I.add), ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API
.jl:66
 [27] add(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\A
PI.jl:66
 [28] top-level scope at REPL[20]:1
caused by [exception 1]
IOError: symlink: operation not permitted (EPERM)
Stacktrace:
 [1] uv_error at .\libuv.jl:97 [inlined]
 [2] symlink(::String, ::String) at .\file.jl:851
 [3] probe_symlink_creation(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\PlatformEngines.jl:131
 [4] #unpack#95(::Bool, ::typeof(Pkg.PlatformEngines.unpack), ::String, ::String) at D:\buildbot\wo
rker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:727
 [5] #unpack at .\logging.jl:0 [inlined]
 [6] #download_verify_unpack#100(::Nothing, ::Bool, ::Bool, ::Bool, ::typeof(Pkg.PlatformEngines.do
wnload_verify_unpack), ::String, ::String, ::String) at D:\buildbot\worker\package_win64\build\usr\
share\julia\stdlib\v1.3\Pkg\src\PlatformEngines.jl:894
 [7] #download_verify_unpack at .\none:0 [inlined]
 [8] #download_artifact#38(::Bool, ::typeof(Pkg.Artifacts.download_artifact), ::Base.SHA1, ::String
, ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts
.jl:744
 [9] #download_artifact at .\none:0 [inlined]
 [10] #ensure_artifact_installed#42(::Pkg.BinaryPlatforms.Platform, ::Bool, ::typeof(Pkg.Artifacts.
ensure_artifact_installed), ::String, ::Dict{String,Any}, ::String) at D:\buildbot\worker\package_w
in64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:869
 [11] (::Pkg.Artifacts.var"#kw##ensure_artifact_installed")(::NamedTuple{(:platform, :verbose),Tupl
e{Pkg.BinaryPlatforms.Windows,Bool}}, ::typeof(Pkg.Artifacts.ensure_artifact_installed), ::String,
::Dict{String,Any}, ::String) at .\none:0
 [12] #ensure_all_artifacts_installed#43(::Pkg.BinaryPlatforms.Platform, ::Nothing, ::Bool, ::Bool,
 ::typeof(Pkg.Artifacts.ensure_all_artifacts_installed), ::String) at D:\buildbot\worker\package_wi
n64\build\usr\share\julia\stdlib\v1.3\Pkg\src\Artifacts.jl:919
 [13] #ensure_all_artifacts_installed at D:\buildbot\worker\package_win64\build\usr\share\julia\std
lib\v1.3\Pkg\src\Operations.jl:0 [inlined]
 [14] #download_artifacts#78(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{String,1}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v
1.3\Pkg\src\Operations.jl:580
 [15] #download_artifacts at .\none:0 [inlined]
 [16] #download_artifacts#73(::Pkg.BinaryPlatforms.Windows, ::Bool, ::typeof(Pkg.Operations.downloa
d_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win64\build\usr\share
\julia\stdlib\v1.3\Pkg\src\Operations.jl:570
 [17] (::Pkg.Operations.var"#kw##download_artifacts")(::NamedTuple{(:platform,),Tuple{Pkg.BinaryPla
tforms.Windows}}, ::typeof(Pkg.Operations.download_artifacts), ::Array{Pkg.Types.PackageSpec,1}) at
 .\none:0
 [18] #add#112(::Bool, ::Pkg.BinaryPlatforms.Windows, ::typeof(Pkg.Operations.add), ::Pkg.Types.Con
text, ::Array{Pkg.Types.PackageSpec,1}, ::Array{Base.UUID,1}) at D:\buildbot\worker\package_win64\b
uild\usr\share\julia\stdlib\v1.3\Pkg\src\Operations.jl:1017
 [19] #add at .\none:0 [inlined]
 [20] #add#25(::Bool, ::Pkg.BinaryPlatforms.Windows, ::Base.Iterators.Pairs{Union{},Union{},Tuple{}
,NamedTuple{,Tuple{}}}, ::typeof(Pkg.API.add), ::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1
}) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:102
 [21] add(::Pkg.Types.Context, ::Array{Pkg.Types.PackageSpec,1}) at D:\buildbot\worker\package_win6
4\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:72
 [22] #add#24 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
69 [inlined]
 [23] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:69 [
inlined]
 [24] #add#21 at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:
67 [inlined]
 [25] add at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API.jl:67 [
inlined]
 [26] #add#20(::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{,Tuple{}}}, ::typeof(Pkg.AP
I.add), ::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\API
.jl:66
 [27] add(::String) at D:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.3\Pkg\src\A
PI.jl:66
 [28] top-level scope at REPL[20]:1

Answer 1

You've assigned a variable (of type Vector{String}) called names in your workspace prior to using DataFrames (Julia will prevent you from doing it after). The error message just tells you that you're trying to use names as function, which it isn't in your workspace.

Answer 2

names(df) should work on a data frame:

julia> using DataFrames

julia> df = DataFrame(:a => [2, 3, 5])
3×1 DataFrame
│ Row │ a     │
│     │ Int64 │
├─────┼───────┤
│ 1   │ 2     │
│ 2   │ 3     │
│ 3   │ 5     │

julia> names(df)
1-element Array{Symbol,1}:
 :a

Can you show us your code and try println(df) as well?