ERROR: MethodError: Cannot `convert` an object of type Missing to an object of type String

General Usage
1

I get this when trying to run

CSV.read("chuckle/random.csv", DataFrame)

But when running the same thing on another CSV in the same directory, it works fine.

2

Can you provide the full stack trace? Also could you report the output of

using Pkg
Pkg.status()
3

Can you try increasing the value of rows_to_check?

So something like this?

CSV.read("chuckle/random.csv", DataFrame; rows_to_check = 100)

Try increasing it to 100 or 500 or 1000?

4

Stacktrace:

ERROR: MethodError: Cannot `convert` an object of type Missing to an object of type String

Closest candidates are:
  convert(::Type{S}, ::CategoricalArrays.CategoricalValue) where S<:Union{AbstractChar, AbstractString, Number}
   @ CategoricalArrays C:\Users\steve\.julia\packages\CategoricalArrays\0yLZN\src\value.jl:92
  convert(::Type{String}, ::WeakRefStrings.WeakRefString)
   @ WeakRefStrings C:\Users\steve\.julia\packages\WeakRefStrings\31nkb\src\WeakRefStrings.jl:81
  convert(::Type{String}, ::FilePathsBase.AbstractPath)
   @ FilePathsBase C:\Users\steve\.julia\packages\FilePathsBase\4RrDh\src\path.jl:117
  ...

Stacktrace:
 [1] get!(default::Function, h::Dict{String, UInt32}, key0::Missing)
   @ Base .\dict.jl:455
 [2] checkpooled!(#unused#::Type{String}, pertaskcolumns::Nothing, col::CSV.Column, j::Int64, ntasks::Int64, nrows::Int64, ctx::CSV.Context)
   @ CSV C:\Users\steve\.julia\packages\CSV\OnldF\src\file.jl:514
 [3] CSV.File(ctx::CSV.Context, chunking::Bool)
   @ CSV C:\Users\steve\.julia\packages\CSV\OnldF\src\file.jl:302
 [4] File
   @ C:\Users\steve\.julia\packages\CSV\OnldF\src\file.jl:227 [inlined]
 [5] #File#32
   @ C:\Users\steve\.julia\packages\CSV\OnldF\src\file.jl:223 [inlined]
 [6] CSV.File(source::String)
   @ CSV C:\Users\steve\.julia\packages\CSV\OnldF\src\file.jl:162
 [7] read(source::String, sink::Type; copycols::Bool, kwargs::Base.Pairs{Symbol, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
   @ CSV C:\Users\steve\.julia\packages\CSV\OnldF\src\CSV.jl:117
 [8] read(source::String, sink::Type)
   @ CSV C:\Users\steve\.julia\packages\CSV\OnldF\src\CSV.jl:113
 [9] top-level scope
   @ c:\julia\process.jl:61

Pkg.status

  [336ed68f] CSV v0.10.11
  [49dc2e85] Calculus v0.5.1       
  [a93c6f00] DataFrames v1.6.1     
  [1313f7d8] DataFramesMeta v0.14.1
  [89b67f3b] ExcelFiles v1.0.0     
⌅ [c04bee98] ExcelReaders v0.11.0  
  [38e38edf] GLM v1.9.0
  [4076af6c] JuMP v1.16.0
  [626c502c] Parquet v0.8.4
  [91a5bcdd] Plots v1.39.0
  [438e738f] PyCall v1.96.2
⌅ [df47a6cb] RData v0.8.3
  [ce6b1742] RDatasets v0.7.7
  [9d95f2ec] TypedTables v1.4.3
⌅ [fdbf4ff8] XLSX v0.7.10
5

Same Error and Stacktrace as in my reply to @mkitti

6

How many lines are in the chuckle/random.csv file?

That is, what is the output of wc -l chuck/random.csv?

7

Stacktrace points to

8

I just realized that OP is on Windows.

For Windows, this should give you the number of lines in the file. Run the following in PowerShell:

(Get-Content random.csv).Length
9

└─$ wc -l c:/data/chuckle/random.csv
2326 c:/data/chuckle/random.csv

10

Can you try this?

CSV.read("chuckle/random.csv", DataFrame; rows_to_check = 2326)

12

Same thing

13

How about this?

CSV.File("chuckle/random.csv"; rows_to_check = 2326)

14

Also, is it possible for you to share the CSV file?

15

can’t share it due to its contents

16

Can you try doing the following?

for i in 1:2326
    @info "Attempting" i
    CSV.File("chuckle/random.csv"; limit = i, ntasks = 1)
    @info "Finished" i
end
17

For clarity, the referenced error seems to indicate that a request was made to convert a Missing value into a string. It seems like the CSV.jl parser might be having some trouble with something in this .csv file that lead to a ::Missing value somewhere unexpected.

1 Like
18

I’ll have to keep that code handy. It helped find what the error was. It stopped on a line where one of the fields was like this:

...","text "text" text","....
3 Likes
19

Good to hear you found the problem.

I wonder if this is worth filing an Issue on the CSV.jl repo? This seems like a relatively unhelpful error message, indicating the direct internal cause of the error (can’t convert missing to string) rather than the more pertinent error: malformed input at line n of the input file.

20

I’ll post there also. And yes, there were no Missing values in the file at all.

2 Likes