# How to read tables out of a MAT file?

**URL:** <https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098>\
**Category:** General Usage\
**Tags:** question, matlab, io\
**Created:** [October 20, 2021, 1:58pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098 "2021-10-20T13:58:36Z")\
**Posts on this page:** 12\
**Page:** 1

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**Author:** ![leon](https://avatars.discourse-cdn.com/v4/letter/l/dc4da7/32.png) [@leon](https://discourse.julialang.org/u/leon)\
**Post date:** [October 20, 2021, 1:58pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/1 "2021-10-20T13:58:36Z")

</div>

Normally, this is how I read a variable out of a MAT file:

```julia
using MAT
F1 = matopen("test.mat");
Var1 = read(F1, "Var1");
close(F1);

```

Now I have some Matlab tables stored in the MAT file. Below is an example:

```julia
 Name Size Bytes Class Attributes
   T1 28206x73 22997697 table

```

How do I read the table T1 out? Once I read it out, how do I access each of the column data?

Here is a test mat file containing a table called T1:

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Many thanks!

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**Author:** ![rafael.guerra](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rafael.guerra/32/216610_2.png) [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)\
**Post date:** [October 20, 2021, 3:47pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/2 "2021-10-20T15:47:40Z")

</div>

Check this example to see if it helps:

```julia
using MAT
M = rand(3,3)
file = matopen("matfile.mat", "w")
write(file, "Mout", M)
close(file)

vars = matread("matfile.mat") # check variable name in Dict is "Mout"
M = vars["Mout"]

3×3 Matrix{Float64}:
 0.0139301 0.538621 0.564867
 0.939367 0.120995 0.0989636
 0.96166 0.902847 0.837158

```

---

<div class="post-metadata">

**Author:** ![rafael.guerra](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rafael.guerra/32/216610_2.png) [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)\
**Post date:** [October 20, 2021, 4:23pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/4 "2021-10-20T16:23:16Z")

</div>

Not familiar with Matlab tables, but they look like dataframes.

However inspecting your file above it shows objects with different lengths?

```julia
vars = matread("test.mat") # check variable names in Dict
dic = vars[" __opaque__"]

Dict{String, Any} with 4 entries:
  "s1" => Int8[77, 67, 79, 83]
  "arr" => ("", UInt32[0xdd000000; 0x00000002; … ; 0x00000001; 0x00000001;;])
  "s0" => Int8[84, 49]
  "s2" => Int8[116, 97, 98, 108, 101]

```

If they were a proper table, then in Julia you could use DataFrames constructor to build a dataframe from the Dict:

```julia
df = DataFrame(dic)

```

Sorry, my limits have been reached here.

---

<div class="post-metadata">

**Author:** ![leon](https://avatars.discourse-cdn.com/v4/letter/l/dc4da7/32.png) [@leon](https://discourse.julialang.org/u/leon)\
**Post date:** [October 20, 2021, 4:28pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/5 "2021-10-20T16:28:26Z")

</div>

Many thanks for the reply!

This is what my table looks like inside Matlab:

T1 =

100×6 table

```
CTDPRES Depth CTDTEMP_ITS90 CTDTEMP_flag CTDSAL_PSS78 CTDSAL_flag
____________  _________________________  _______________________

  115 113.9 2.199 2 32.761 2     
  101 100.1 2.098 2 32.739 2     
   60 59.4 1.637 2 32.662 2     
   42 41.6 0.763 2 32.515 2     
   31 30.7 -0.318 2 32.217 2     
   20 19.8 -0.45 2 32.156 2     
   11 10.9 -0.444 2 32.158 2     
    5 5 -0.44 2 32.158 2     
  102 101 1.302 2 32.598 2

```

---

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**Author:** ![rafael.guerra](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rafael.guerra/32/216610_2.png) [@rafael.guerra](https://discourse.julialang.org/u/rafael.guerra)\
**Post date:** [October 20, 2021, 4:55pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/6 "2021-10-20T16:55:18Z")

</div>

It seems that MATLAB tables are not supported by the MAT.jl package, [see here.](https://github.com/JuliaIO/MAT.jl/issues/127)

---

<div class="post-metadata">

**Author:** ![leon](https://avatars.discourse-cdn.com/v4/letter/l/dc4da7/32.png) [@leon](https://discourse.julialang.org/u/leon)\
**Post date:** [October 20, 2021, 4:58pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/7 "2021-10-20T16:58:37Z")

</div>

So bad the MAT package can’t do it now. I hope someone will make this happen soon.

---

<div class="post-metadata">

**Author:** ![cchderrick](https://avatars.discourse-cdn.com/v4/letter/c/ecd19e/32.png) [@cchderrick](https://discourse.julialang.org/u/cchderrick)\
**Post date:** [October 20, 2021, 8:00pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/8 "2021-10-20T20:00:36Z")

</div>

This doesn’t do what you wanted, load a table from MAT file. But I wanted to see if it is possible with MATLAB.jl (needs a MATLAB installation)  
Basically I had to use MATLAB to do all the data conversion to data types that are supported: convert the table content to cell, convert headers to array of string. Then, rebuild it with DataFrame.

```julia
using MATLAB
using DataFrames
mxcall(:load,0,"patients")
mat"patients = table(Gender,Age,Height,Weight,Smoker,Systolic,Diastolic);"
data = mat"table2cell(patients)"
headers = mat"patients.Properties.VariableNames"
df = DataFrame([headers[c]=>data[:,c] for c in 1:length(headers)])

```

```julia
julia> df
100×8 DataFrame
 Row │ LastName Gender Age Height Weight Smoker Systolic Diastolic
     │ Any Any Any Any Any Any Any Any
─────┼───────────────────────────────────────────────────────────────────────
   1 │ Smith Male 38.0 71.0 176.0 true 124.0 93.0
   2 │ Johnson Male 43.0 69.0 163.0 false 109.0 77.0
   3 │ Williams Female 38.0 64.0 131.0 false 125.0 83.0
   4 │ Jones Female 40.0 67.0 133.0 false 117.0 75.0
   5 │ Brown Female 49.0 64.0 119.0 false 122.0 80.0
   6 │ Davis Female 46.0 68.0 142.0 false 121.0 70.0
   7 │ Miller Female 33.0 64.0 142.0 true 130.0 88.0
   8 │ Wilson Male 40.0 68.0 180.0 false 115.0 82.0
   9 │ Moore Male 28.0 68.0 183.0 false 115.0 78.0
  10 │ Taylor Female 31.0 66.0 132.0 false 118.0 86.0
  11 │ Anderson Female 45.0 68.0 128.0 false 114.0 77.0
  12 │ Thomas Female 42.0 66.0 137.0 false 115.0 68.0
  13 │ Jackson Male 25.0 71.0 174.0 false 127.0 74.0
  14 │ White Male 39.0 72.0 202.0 true 130.0 95.0
  ⋮ │ ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ ⋮
  88 │ Hughes Female 49.0 63.0 123.0 true 128.0 96.0
  89 │ Flores Female 31.0 66.0 141.0 true 123.0 87.0
  90 │ Washington Female 37.0 65.0 129.0 false 122.0 81.0
  91 │ Butler Male 38.0 68.0 184.0 true 138.0 90.0
  92 │ Simmons Male 45.0 71.0 181.0 false 124.0 77.0
  93 │ Foster Female 30.0 70.0 124.0 false 130.0 91.0
  94 │ Gonzales Male 48.0 71.0 174.0 false 123.0 79.0
  95 │ Bryant Female 48.0 66.0 134.0 false 129.0 73.0
  96 │ Alexander Male 25.0 69.0 171.0 true 128.0 99.0
  97 │ Russell Male 44.0 69.0 188.0 true 124.0 92.0
  98 │ Griffin Male 49.0 70.0 186.0 false 119.0 74.0
  99 │ Diaz Male 45.0 68.0 172.0 true 136.0 93.0
 100 │ Hayes Male 48.0 66.0 177.0 false 114.0 86.0
                                                              73 rows omitted

```

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**Author:** ![mbauman](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mbauman/32/31082_2.png) [@mbauman](https://discourse.julialang.org/u/mbauman)\
**Post date:** [October 20, 2021, 8:06pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/9 "2021-10-20T20:06:05Z")

</div>

I’ve long ceased needing to read Matlab files, but I fear my work from 2014 might still be state of the art.

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In short, I’d bet tables (which are newer than that work) are just Matlab class objects. And thus they get saved in that same undocumented manner as I was attempting to reverse-engineer above. See also [this python question](https://stackoverflow.com/questions/15512560/access-mat-file-containing-matlab-classes-in-python) seeking the same thing.

---

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**Author:** ![leon](https://avatars.discourse-cdn.com/v4/letter/l/dc4da7/32.png) [@leon](https://discourse.julialang.org/u/leon)\
**Post date:** [October 20, 2021, 8:58pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/10 "2021-10-20T20:58:26Z")

</div>

Many thanks, Derrick!

You used “0” and “paitents”. I’m not sure what they are. If my MAT file is located here: `F1 = "/Path/test.mat");`

And the table that is stored within this mat file is called T1. How would I write this code to read out T1?

---

<div class="post-metadata">

**Author:** ![cchderrick](https://avatars.discourse-cdn.com/v4/letter/c/ecd19e/32.png) [@cchderrick](https://discourse.julialang.org/u/cchderrick)\
**Post date:** [October 21, 2021, 3:34pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/11 "2021-10-21T15:34:54Z")

</div>

Some quick usage:  
[https://github.com/JuliaInterop/MATLAB.jl#use-matlab-engine](https://github.com/JuliaInterop/MATLAB.jl#use-matlab-engine)

I chose to use `mxcall` and `mat""`just out of my preference.  
So here is the MATLAB evaluation I wanted

```julia
load('patients')

```

this is an example table dataset came with MATLAB (found it in `table` doc)

`mxcall` has this signature:

1. the MATLAB function you wish to call as a symbol, in this case, it is `:load`
2. number of output I am expecting, in this case, I just want to load it into workspace, so its is 0
3. the arguments, it is a string in MATLAB, so I could define it in Julia string, which is supported for conversion

so in your case, I would guess it is this:

```julia
mxcall(:load, 0, "/Path/test.mat")
data = mat"table2cell(T1)"
headers = mat"T1.Properties.VariableNames"
df = DataFrame([headers[c]=>data[:,c] for c in 1:length(headers)])

```

---

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**Author:** ![leon](https://avatars.discourse-cdn.com/v4/letter/l/dc4da7/32.png) [@leon](https://discourse.julialang.org/u/leon)\
**Post date:** [October 21, 2021, 4:07pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/12 "2021-10-21T16:07:00Z")

</div>

> [@cchderrick](#):
>
> ```julia
> mxcall(:load, 0, "/Path/test.mat")
> data = mat"table2cell(T1)"
> headers = mat"T1.Properties.VariableNames"
> df = DataFrame([headers[c]=>data[:,c] for c in 1:length(headers)])
> 
> ```

Many thanks! Unfortunately, I’m getting the below error:

```julia
LoadError: MATLAB.MEngineError("failed to get variable ans from MATLAB session")

Stacktrace:

[1] **get_mvariable(** session::MSession, name::Symbol **)**
@ MATLAB ~/.julia/packages/MATLAB/T20Ly/src/engine.jl:164
[2] **get_mvariable**
@ ~/.julia/packages/MATLAB/T20Ly/src/engine.jl:168 [inlined]
[3] **get_variable(** name::Symbol **)**
@ MATLAB ~/.julia/packages/MATLAB/T20Ly/src/engine.jl:170
[4] top-level scope
@ ~/.julia/packages/MATLAB/T20Ly/src/matstr.jl:169

```

---

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**Author:** ![cchderrick](https://avatars.discourse-cdn.com/v4/letter/c/ecd19e/32.png) [@cchderrick](https://discourse.julialang.org/u/cchderrick)\
**Post date:** [October 21, 2021, 8:55pm UTC](https://discourse.julialang.org/t/how-to-read-tables-out-of-a-mat-file/70098/13 "2021-10-21T20:55:00Z")

</div>

The error suggested that one or both of these line didn’t return a variable `ans`

```julia
data = mat"table2cell(T1)"
headers = mat"T1.Properties.VariableNames"

```

`MATLAB.jl` basically a non-desktop session of MATLAB, after the load command, you could do this to see if it load the data into workspace.

```julia
mat"whos"

```

By the way, I forgot a command in my earlier post.  
FYI, I have R2017.