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

csvread(filename) reads real or complex numeric data from comma-separated text files and returns a dense double matrix. Row and column controls are zero-based.

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. The public forms are a four-element numeric range [r1 c1 r2 c2] or an A1 range such as "B2..D6". RunMat's colon-separated A1 range and two-element numeric range are independent compatibility-gated extensions.
• 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.
• Real input produces a dense double tensor; any complex token (a+bi, a+bj, or a pure-imaginary form) produces a complex-double tensor without discarding an all-zero imaginary component. 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 file I/O and parsing on the host CPU. Public host controls require no provider. With the csvread-resident-control-inputs extension enabled, resident controls are gathered through their owning provider; the resulting tensor still returns in host memory.

GPU memory and residency

csvread always returns a host-resident tensor because it performs file I/O and parsing on the CPU. Resident filename, offset, and range controls are accepted only when the csvread-resident-control-inputs RunMat extension is enabled.

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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