# How to get type of a column using Tables.Schema from Tables.jl?

**URL:** <https://discourse.julialang.org/t/how-to-get-type-of-a-column-using-tables-schema-from-tables-jl/108432>\
**Category:** Data\
**Tags:** type, tables\
**Created:** [January 6, 2024, 11:48am UTC](https://discourse.julialang.org/t/how-to-get-type-of-a-column-using-tables-schema-from-tables-jl/108432 "2024-01-06T11:48:18Z")\
**Posts on this page:** 8\
**Page:** 1

<div class="post-metadata">

**Author:** ![FemtoTrader](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/femtotrader/32/309_2.png) [@FemtoTrader](https://discourse.julialang.org/u/FemtoTrader)\
**Post date:** [January 6, 2024, 11:48am UTC](https://discourse.julialang.org/t/how-to-get-type-of-a-column-using-tables-schema-from-tables-jl/108432/1 "2024-01-06T11:48:18Z")

</div>

Hello,

I have a `TSFrame` like so

```julia
julia> table
50×5 TSFrame with Date Index
 Index Open High Low Close Volume
 Date Float64 Float64 Float64 Float64 Float64
─────────────────────────────────────────────────────────
 2020-01-01 10.81 11.02 9.9 10.5 55.03
 2020-01-02 10.58 10.74 9.78 9.78 117.86
 2020-01-03 10.07 10.65 9.5 10.46 301.04
 2020-01-04 10.58 11.05 10.47 10.51 157.94
 2020-01-05 10.56 10.7 10.26 10.55 39.96
 2020-01-06 10.4 10.73 10.4 10.72 42.87
 2020-01-07 10.74 11.16 10.12 10.16 191.95
 2020-01-08 10.16 10.86 9.91 10.25 55.09
 2020-01-09 10.29 10.29 9.4 9.4 131.58
 2020-01-10 9.4 10.8 9.11 9.5 249.69
 2020-01-11 9.62 9.62 9.12 9.23 77.75
 2020-01-12 9.35 9.35 8.5 8.5 197.33
 2020-01-13 8.64 9.43 8.55 8.8 107.93
 2020-01-14 8.8 8.91 8.21 8.33 35.86
 2020-01-15 8.31 8.84 7.34 7.53 269.05
 2020-01-16 7.56 7.82 7.53 7.61 34.18
 2020-01-17 7.61 7.61 6.5 6.78 209.1
 2020-01-18 7.04 8.84 7.04 8.6 241.95
 2020-01-19 8.56 9.42 8.15 9.21 162.86
 2020-01-20 9.26 9.5 8.72 8.95 112.99
 2020-01-21 8.95 9.29 8.6 9.22 66.53
 2020-01-22 9.31 9.4 8.89 9.1 87.5
 2020-01-23 9.1 9.1 8.14 8.31 349.14
 2020-01-24 8.51 8.51 8.24 8.37 44.38
 2020-01-25 8.42 8.95 8.06 8.3 45.79
 2020-01-26 8.3 8.7 7.7 7.78 139.4
 2020-01-27 7.87 8.95 7.87 8.05 46.49
 2020-01-28 7.94 8.75 7.94 8.1 27.45
 2020-01-29 8.1 8.39 8.0 8.08 16.44
 2020-01-30 8.08 8.28 7.37 7.49 83.54
 2020-01-31 7.49 7.58 7.49 7.58 15.08
 2020-02-01 7.4 8.17 7.38 8.17 60.72
 2020-02-02 8.09 8.83 8.05 8.83 140.22
 2020-02-03 8.86 9.2 8.79 8.91 171.6
 2020-02-04 8.81 9.25 8.67 9.2 209.26
 2020-02-05 9.16 10.1 9.16 9.76 199.2
 2020-02-06 9.69 9.88 8.9 9.42 165.77
 2020-02-07 9.45 9.65 9.17 9.3 61.71
 2020-02-08 9.18 9.32 8.6 9.32 29.73
 2020-02-09 9.4 9.4 8.92 9.04 12.93
 2020-02-10 9.0 9.01 8.99 9.0 4.14
 2020-02-11 9.11 9.36 9.11 9.33 12.45
 2020-02-12 9.23 9.46 9.11 9.34 42.23
 2020-02-13 9.34 9.34 8.43 8.49 133.29
 2020-02-14 8.49 9.4 8.42 9.21 120.02
 2020-02-15 9.3 10.5 9.26 10.15 255.3
 2020-02-16 10.23 10.3 10.0 10.3 111.55
 2020-02-17 10.29 10.86 10.19 10.59 108.27
 2020-02-18 10.77 10.77 10.15 10.23 48.29
 2020-02-19 10.28 10.39 9.62 10.0 81.66

```

I get the `Tables.Schema` using

```julia
julia> sch = Tables.schema(table)
Tables.Schema:
 :Index Date
 :Open Float64
 :High Float64
 :Low Float64
 :Close Float64
 :Volume Float64

julia> sch.
names
types
julia> sch.names
(:Index, :Open, :High, :Low, :Close, :Volume)

julia> sch.types
(Date, Float64, Float64, Float64, Float64, Float64)

julia> fieldnames(typeof(sch))
(:storednames, :storedtypes)

julia> methodswith(typeof(sch))
0-element Vector{Method}

```

I wonder what is the correct manner to get type of column `:Close` (if this column exists).

Kind regards

---

<div class="post-metadata">

**Author:** ![bkamins](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bkamins/32/208538_2.png) [@bkamins](https://discourse.julialang.org/u/bkamins)\
**Post date:** [January 6, 2024, 2:52pm UTC](https://discourse.julialang.org/t/how-to-get-type-of-a-column-using-tables-schema-from-tables-jl/108432/2 "2024-01-06T14:52:47Z")

</div>

Just as you do. Quoting the documentation:

> To access the names, one can simply call `sch.names` to return a collection of Symbols (`Tuple` or `Vector`). To access column element types, one can similarly call `sch.types`, which will return a collection of  
> types (like (`Int64`, `Float64`, `String`)).

---

<div class="post-metadata">

**Author:** ![rocco\_sprmnt21](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rocco_sprmnt21/32/20127_2.png) [@rocco\_sprmnt21](https://discourse.julialang.org/u/rocco_sprmnt21)\
**Post date:** [January 6, 2024, 3:07pm UTC](https://discourse.julialang.org/t/how-to-get-type-of-a-column-using-tables-schema-from-tables-jl/108432/3 "2024-01-06T15:07:55Z")

</div>

```julia
sch[sch.names.==:close,:types]

```

**not tested**

or

```julia
eltype(table.close)

```

---

<div class="post-metadata">

**Author:** ![FemtoTrader](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/femtotrader/32/309_2.png) [@FemtoTrader](https://discourse.julialang.org/u/FemtoTrader)\
**Post date:** [January 6, 2024, 8:04pm UTC](https://discourse.julialang.org/t/how-to-get-type-of-a-column-using-tables-schema-from-tables-jl/108432/4 "2024-01-06T20:04:01Z")

</div>

```
sch[sch.names.==:Close,:types]

```

doesn’t work. It raises

```julia
ERROR: MethodError: no method matching getindex(::Tables.Schema{(:Index, :Open, :High, :Low, :Close, :Volume), Tuple{…}}, ::NTuple{6, Bool}, ::Symbol)
Stacktrace:
 [1] top-level scope
   @ REPL[28]:1
Some type information was truncated. Use `show(err)` to see complete types.

```

```
eltype(table.Close)

```

works only is table is a TSFrame or DataFrame. Not if it’s an other sort of table compatible with Tables.jl such as RT\_OHLCV or CT\_OHLCV with

```julia
const OPEN_TMPL = [
    10.81,
    10.58,
    10.07,
    10.58,
    10.56,
    10.4,
    10.74,
    10.16,
    10.29,
    9.4,
    9.62,
    9.35,
    8.64,
    8.8,
    8.31,
    7.56,
    7.61,
    7.04,
    8.56,
    9.26,
    8.95,
    9.31,
    9.1,
    8.51,
    8.42,
    8.3,
    7.87,
    7.94,
    8.1,
    8.08,
    7.49,
    7.4,
    8.09,
    8.86,
    8.81,
    9.16,
    9.69,
    9.45,
    9.18,
    9.4,
    9.0,
    9.11,
    9.23,
    9.34,
    8.49,
    9.3,
    10.23,
    10.29,
    10.77,
    10.28,
]
const HIGH_TMPL = [
    11.02,
    10.74,
    10.65,
    11.05,
    10.7,
    10.73,
    11.16,
    10.86,
    10.29,
    10.8,
    9.62,
    9.35,
    9.43,
    8.91,
    8.84,
    7.82,
    7.61,
    8.84,
    9.42,
    9.5,
    9.29,
    9.4,
    9.1,
    8.51,
    8.95,
    8.7,
    8.95,
    8.75,
    8.39,
    8.28,
    7.58,
    8.17,
    8.83,
    9.2,
    9.25,
    10.1,
    9.88,
    9.65,
    9.32,
    9.4,
    9.01,
    9.36,
    9.46,
    9.34,
    9.4,
    10.5,
    10.3,
    10.86,
    10.77,
    10.39,
]
const LOW_TMPL = [
    9.9,
    9.78,
    9.5,
    10.47,
    10.26,
    10.4,
    10.12,
    9.91,
    9.4,
    9.11,
    9.12,
    8.5,
    8.55,
    8.21,
    7.34,
    7.53,
    6.5,
    7.04,
    8.15,
    8.72,
    8.6,
    8.89,
    8.14,
    8.24,
    8.06,
    7.7,
    7.87,
    7.94,
    8.0,
    7.37,
    7.49,
    7.38,
    8.05,
    8.79,
    8.67,
    9.16,
    8.9,
    9.17,
    8.6,
    8.92,
    8.99,
    9.11,
    9.11,
    8.43,
    8.42,
    9.26,
    10.0,
    10.19,
    10.15,
    9.62,
]
const CLOSE_TMPL = [
    10.5,
    9.78,
    10.46,
    10.51,
    10.55,
    10.72,
    10.16,
    10.25,
    9.4,
    9.5,
    9.23,
    8.5,
    8.8,
    8.33,
    7.53,
    7.61,
    6.78,
    8.6,
    9.21,
    8.95,
    9.22,
    9.1,
    8.31,
    8.37,
    8.3,
    7.78,
    8.05,
    8.1,
    8.08,
    7.49,
    7.58,
    8.17,
    8.83,
    8.91,
    9.2,
    9.76,
    9.42,
    9.3,
    9.32,
    9.04,
    9.0,
    9.33,
    9.34,
    8.49,
    9.21,
    10.15,
    10.3,
    10.59,
    10.23,
    10.0,
]

const VOLUME_TMPL = [
    55.03,
    117.86,
    301.04,
    157.94,
    39.96,
    42.87,
    191.95,
    55.09,
    131.58,
    249.69,
    77.75,
    197.33,
    107.93,
    35.86,
    269.05,
    34.18,
    209.1,
    241.95,
    162.86,
    112.99,
    66.53,
    87.5,
    349.14,
    44.38,
    45.79,
    139.4,
    46.49,
    27.45,
    16.44,
    83.54,
    15.08,
    60.72,
    140.22,
    171.6,
    209.26,
    199.2,
    165.77,
    61.71,
    29.73,
    12.93,
    4.14,
    12.45,
    42.23,
    133.29,
    120.02,
    255.3,
    111.55,
    108.27,
    48.29,
    81.66,
]

const CLOSE_EQUAL_VALUES_TMPL = repeat([10.46], length(CLOSE_TMPL))

using Dates
const DATE_TMPL =
    collect(range(Dates.Date(2020, 1, 1), step = Dates.Day(1), length = length(CLOSE_TMPL)))

const CT_OHLCV = (Index=DATE_TMPL, Open=OPEN_TMPL, High=HIGH_TMPL, Low=LOW_TMPL, Close=CLOSE_TMPL, Volume=VOLUME_TMPL)

const RT_OHLCV = [(Index=DATE_TMPL[i], Open=OPEN_TMPL[i], High=HIGH_TMPL[i], Low=LOW_TMPL[i], Close=CLOSE_TMPL[i], Volume=VOLUME_TMPL[i]) for i in 1:length(CLOSE_TMPL)]

```

---

<div class="post-metadata">

**Author:** ![FemtoTrader](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/femtotrader/32/309_2.png) [@FemtoTrader](https://discourse.julialang.org/u/FemtoTrader)\
**Post date:** [January 6, 2024, 8:07pm UTC](https://discourse.julialang.org/t/how-to-get-type-of-a-column-using-tables-schema-from-tables-jl/108432/5 "2024-01-06T20:07:39Z")

</div>

I think I have a solution using…

```
julia> sch.types[argmax((sch.names.==:Close))]
Float64

```

But if you have a better one please tell me.

---

<div class="post-metadata">

**Author:** ![Dan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dan/32/42581_2.png) [@Dan](https://discourse.julialang.org/u/Dan)\
**Post date:** [January 6, 2024, 8:30pm UTC](https://discourse.julialang.org/t/how-to-get-type-of-a-column-using-tables-schema-from-tables-jl/108432/6 "2024-01-06T20:30:33Z")

</div>

I think this is the way you are looking for:

```julia
Tables.columntype(sch, :Close)

```

If used a lot, then:

```julia
import Tables: columntype

```

can remove the need for a Module prefix.

---

<div class="post-metadata">

**Author:** ![FemtoTrader](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/femtotrader/32/309_2.png) [@FemtoTrader](https://discourse.julialang.org/u/FemtoTrader)\
**Post date:** [January 6, 2024, 8:47pm UTC](https://discourse.julialang.org/t/how-to-get-type-of-a-column-using-tables-schema-from-tables-jl/108432/7 "2024-01-06T20:47:49Z")

</div>

Thanks @Dan and all

---

<div class="post-metadata">

**Author:** ![rocco\_sprmnt21](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rocco_sprmnt21/32/20127_2.png) [@rocco\_sprmnt21](https://discourse.julialang.org/u/rocco_sprmnt21)\
**Post date:** [January 6, 2024, 11:22pm UTC](https://discourse.julialang.org/t/how-to-get-type-of-a-column-using-tables-schema-from-tables-jl/108432/8 "2024-01-06T23:22:24Z")

</div>

```julia
sch.types[findfirst(sch.names.==:Close)]

```

```julia
Dict(Pair.(sch.names,sch.types))[:Close]

```

to make it a little more generic

```julia
gp(sch)=getproperty.(Ref(sch), propertynames(sch))
Dict(zip(gp(sch)...))[:Close]

```