csvread — Read numeric data from CSV files in MATLAB and RunMat.

csvread(filename) reads numeric data from comma-separated text files and returns a dense double matrix. Legacy row/column offset handling (including zero-based forms) follows MATLAB and RunMat compatibility behavior.

Syntax

M = csvread(filename)
M = csvread(filename, row, col)
M = csvread(filename, row, col, range)

Inputs

Returns

Errors

How csvread works

• Accepts character vectors or string scalars for the file name. String arrays must contain exactly one element.
• csvread(filename, row, col) starts reading at the zero-based row row and column col, skipping any data before that offset.
• csvread(filename, row, col, range) reads only the rectangle described by range. Numeric ranges must contain four elements [r1 c1 r2 c2] (zero-based, inclusive). Excel-style ranges use the familiar "B2:D6" A1 notation, which RunMat converts to zero-based indices internally.
• Empty fields (two consecutive commas or a trailing comma) are interpreted as 0. Tokens such as NaN, Inf, and -Inf are accepted (case-insensitive).
• Any other nonnumeric token raises an error that identifies the offending row and column.
• File input is read as byte-oriented CSV text before numeric parsing, so non-UTF-8 bytes in skipped header rows or skipped label columns do not cause an I/O decoding failure.
• Results are dense double-precision tensors using column-major layout. An empty file produces a 0×0 tensor.
• Paths can contain ~ to reference the home directory; RunMat expands the token before opening the file.

Does RunMat run csvread on the GPU?

csvread performs all work on the host CPU. Arguments are gathered from the GPU when necessary, and the resulting tensor is returned in host memory. To keep data on the GPU, call gpuArray on the output or switch to readmatrix with the 'Like' option. No provider hooks are required.

GPU memory and residency

csvread always returns a host-resident tensor because it performs file I/O and parsing on the CPU. If you need the data on the GPU, wrap the call with gpuArray(csvread(...)) or switch to readmatrix with the 'Like' option so that RunMat can place the result directly on the desired device.

Examples

Import Entire CSV File

writematrix([1 2 3; 4 5 6], "scores.csv");
M = csvread("scores.csv");
disp(M);
delete("scores.csv")

Expected output:

M =
     1     2     3
     4     5     6

Skip Header Row And Column Using Zero-Based Offsets

fid = fopen("with_header.csv", "w");
fprintf(fid, "Name,Jan,Feb\nalpha,1,2\nbeta,3,4\n");
fclose(fid);

M = csvread("with_header.csv", 1, 1);
disp(M);
delete("with_header.csv");

Expected output:

M =
     1     2
     3     4

Read A Specific Range With Numeric Vector Syntax

fid = fopen("measurements.csv", "w");
fprintf(fid, "10,11,12,13\n14,15,16,17\n18,19,20,21\n22,23,24,25\n");
fclose(fid);

block = csvread("measurements.csv", 0, 0, [1 1 2 3])
delete("measurements.csv");

Expected output:

block =
    15    16    17
    19    20    21

Read A Block Using Excel-Style Range Notation

fid = fopen("measurements2.csv", "w");
fprintf(fid, "10,11,12\n14,15,16\n18,19,20\n");
fclose(fid);

sub = csvread("measurements2.csv", 0, 0, "B2:C3")
delete("measurements2.csv");

Expected output:

sub =
    15    16
    19    20

Handle Empty Fields As Zeros

fid = fopen("with_blanks.csv", "w");
fprintf(fid, "1,,3\n,5,\n7,8,\n");
fclose(fid);

M = csvread("with_blanks.csv")
delete("with_blanks.csv");

Expected output:

M =
     1     0     3
     0     5     0
     7     8     0

Read Numeric Data From A File In The Home Directory

homePath = fullfile(getenv("HOME"), "runmat_csvread_home.csv");
fid = fopen(homePath, "w");
fprintf(fid, "9,10\n11,12\n");
fclose(fid);

M = csvread(fullfile("~", "runmat_csvread_home.csv"), 0, 0);
disp(M);
delete(homePath);

Expected output:

M =
     9    10
    11    12

Detect Errors When Text Appears In Numeric Columns

fid = fopen("bad.csv", "w");
fprintf(fid, "1,2,3\n4,error,6\n");
fclose(fid);

try
    csvread("bad.csv");
catch err
    disp(err.message);
end
delete("bad.csv");

Expected output:

csvread: nonnumeric token error at row 2 column 2

Using csvread with coding agents

Open a RunMat example with live inputs, then ask the agent to explain how csvread changes the result.

FAQ

Related Io functions

Open-source implementation

Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how csvread is executed, line by line, in Rust.

• View the source for csvread in Rust on GitHub
• Learn how the RunMat runtime works
• Found a bug? Open an issue with a minimal reproduction.

About RunMat

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