"readmatirx" does not read the expected data?

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cui,xingxing
cui,xingxing 2021-11-15
评论： cui,xingxing 2025-2-3
My data is 1×51 size in csv, when I use readmatrix function to specify "Range" to import 1 to 50 data, it is empty, or import other range data, the result is all data, my sample code is as follows, thanks in advance! （The "T2.csv" is in the attachment）
T2 = readmatrix("T2.csv","Range","B1:AY1") % empty ???
T2 =
[]
T2 = readmatrix("T2.csv","Range","A1:E1") % all data is imported ???
T2 =
Columns 1 through 12
0 1.0000 0.7382 0.5086 0.3818 0.3015 0.2462 0.2058 0.1750 0.1509 0.1316 0.1157
Columns 13 through 24
0.1025 0.0914 0.0819 0.0736 0.0665 0.0602 0.0547 0.0498 0.0454 0.0415 0.0380 0.0347
Columns 25 through 36
0.0318 0.0292 0.0267 0.0245 0.0225 0.0206 0.0188 0.0172 0.0157 0.0143 0.0130 0.0117
Columns 37 through 48
0.0106 0.0095 0.0085 0.0076 0.0067 0.0058 0.0050 0.0043 0.0036 0.0029 0.0023 0.0016
Columns 49 through 51
0.0011 0.0005 0
T2 = readmatrix("T2.csv","Range","B1:E1") % also empty ???
T2 =
[]
The results of the above experiment are very strange, but the import of data from "range" using the "xlsread" function is normal
  1 个评论
KSSV
KSSV 2021-11-15
Why to specufy posititon? Read whole matrix and pick the required one using indexing.

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Vedant Shah
Vedant Shah 2025-2-3
Hi @cui,xingxing,
Upon analysing the attached .csv file, I noticed that the data is separated by commas (,), whereas the default delimiter used in the “readmatrix” function is a semicolon (;). Since the delimiter was not specified as a comma, it gave unexpected outcomes, such as importing all data or returning an empty array.
To determine the delimiter used in any file, you can open the file as text and observe how the data is separated.
By specifying the delimiter as a comma in the code, we can achieve the desired results. The modified code is as follows:
T2 = readmatrix("T2.csv", 'Range', 'B1:AY1', 'Delimiter', ',');
T2 = readmatrix("T2.csv","Range","A1:E1", 'Delimiter', ',');
T2 = readmatrix("T2.csv","Range","B1:E1", 'Delimiter', ',');
This will provide the desired output as below:
For more information about delimiters, you can refer the following “readmatrix” documentation:
https://in.mathworks.com/help/releases/R2021a/matlab/ref/readmatrix.html
  2 个评论
Stephen23
Stephen23 2025-2-3
Ran in:
"I noticed that the data is separated by commas (,), whereas the default delimiter used in the “readmatrix” function is a semicolon (;)"
No, this is incorrect. READMATRIX does not have a default delimiter, it actually automagically determines the delimiter from the file content. The READMATRIX states "The readmatrix function performs automatic detection of import parameters for your file", which includes detecting the delimiter character.
M = readmatrix('T2.csv')
M = 1×51
0 1.0000 0.7382 0.5086 0.3818 0.3015 0.2462 0.2058 0.1750 0.1509 0.1316 0.1157 0.1025 0.0914 0.0819 0.0736 0.0665 0.0602 0.0547 0.0498 0.0454 0.0415 0.0380 0.0347 0.0318 0.0292 0.0267 0.0245 0.0225 0.0206
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M = readmatrix('T2.csv', 'Range', 'B1:AY1')
M = 1×50
1.0000 0.7382 0.5086 0.3818 0.3015 0.2462 0.2058 0.1750 0.1509 0.1316 0.1157 0.1025 0.0914 0.0819 0.0736 0.0665 0.0602 0.0547 0.0498 0.0454 0.0415 0.0380 0.0347 0.0318 0.0292 0.0267 0.0245 0.0225 0.0206 0.0188
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
readmatrix("T2.csv", "Range","A1:E1")
ans = 1×5
0 1.0000 0.7382 0.5086 0.3818
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
readmatrix("T2.csv", "Range","B1:E1")
ans = 1×4
1.0000 0.7382 0.5086 0.3818
<mw-icon class=""></mw-icon>
<mw-icon class=""></mw-icon>
Given that the file extension CSV stands for "Comma-separated values" and the comma is by far the most common separator character in the USA where MATLAB is developed and sold, not handling commas (as this answer incorrectly claims) would be a very very poor design decision. Of course there are certainly cases where the file content may confuse the heuristics used to automgically determine the delimiter, but I doubt that this is the case for this very simple file content:
type T2.csv
0.0,1.0,0.738173537690035,0.5085718945625297,0.3818114833781992,0.30152288811815803,0.2461633975711672,0.2057571692109543,0.1750339123047904,0.15094004189111568,0.13158166090227272,0.11572100222240495,0.10251478388290215,0.09136870756110145,0.08185200024083146,0.07364491264917741,0.06650522573304661,0.060246186819108385,0.054721567596416595,0.049815298384133094,0.0454341231180433,0.04150229607214739,0.03795768797503274,0.03474888352185092,0.03183298817969899,0.029173950305950897,0.02674126291374525,0.02450894872671965,0.02245475911045516,0.020559536225688776,0.018806700992361258,0.017181838927628434,0.015672362780666613,0.014267235909965733,0.012956744065336624,0.01173230601377595,0.010586315542220533,0.00951200896266189,0.008503353465953548,0.007554952613749239,0.006661965991776031,0.005820040622406393,0.005025252187590046,0.004274054472562578,0.003563235727400815,0.002889880873406134,0.0022513386666593326,0.001645193081279825,0.0010692382971869499,0.000521456777146142,0.0

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