dlmread — Read numeric data from delimiter-separated text files in MATLAB and RunMat.

dlmread(filename) reads numeric data from delimiter-separated ASCII text files. Custom delimiter, range, and offset forms follow MATLAB and RunMat compatibility semantics.

Syntax

M = dlmread(filename)
M = dlmread(filename, delimiter)
M = dlmread(filename, row, col)
M = dlmread(filename, delimiter, range)
M = dlmread(filename, delimiter, row, col)
M = dlmread(filename, delimiter, row, col, range)

Inputs

Returns

Errors

How dlmread works

• Accepts character vectors or string scalars for filename. String arrays must contain exactly one element.
• The delimiter is optional. RunMat detects commas and otherwise treats repeated whitespace as one delimiter. An empty character vector or empty string scalar is the documented placeholder for this automatic delimiter behavior in forms such as dlmread(filename,'',R,C). Nonempty explicit delimiters use character vectors or string scalars. Numeric delimiter character codes are a named RunMat extension and reject in strict compatibility mode.
• The strict-compatible omitted-delimiter offset form is dlmread(filename,'',R,C), where the empty placeholder requests automatic delimiter detection. Raw dlmread(filename,R,C) is a named RunMat-only shorthand. A nonempty delimiter can be supplied as dlmread(filename,delimiter,R,C); all forms use zero-based offsets and skip earlier rows or columns.
• Documented zero-based row, column, and numeric range components accept double, single, or any of the eight integer classes. Typed integers are decoded from authoritative storage and must fit the host index type.
• Spreadsheet ranges use forms such as "A1..B7". Colon spreadsheet notation is a separately named RunMat extension; omitted-delimiter ranges and offsets, two-element numeric start ranges, and offset-plus-range composition are also named extensions.
• Empty fields (for example two adjacent delimiters) 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 using one-based indices (matching MATLAB diagnostic messages).
• Results are dense double-precision tensors laid out in column-major order. Empty files yield a 0×0 tensor.
• Leading UTF-8 byte order marks (BOM) are stripped automatically to match MATLAB's handling of spreadsheets that emit BOM-prefixed text files.
• Paths may include ~ to reference the home directory; RunMat expands the token before opening the file.

Does RunMat run dlmread on the GPU?

dlmread performs file I/O and parsing on the CPU. Resident arguments are gathered only when RunMat extensions are enabled, and the output tensor lives in host memory.

GPU memory and residency

dlmread always creates a CPU-resident tensor because the function performs file I/O synchronously on the host. If you need the data on the GPU, call gpuArray(dlmread(...)) or switch to readmatrix with the 'Like' option to direct the result to a device.

Examples

Reading comma-delimited data by default

writematrix([1 2 3; 4 5 6], "samples.csv");
M = dlmread("samples.csv")
delete("samples.csv");

Expected output:

M =
     1     2     3
     4     5     6

Importing semicolon-separated values

fid = fopen("scores.txt", "w");
fprintf(fid, "1;2;3\n4;5;6\n");
fclose(fid);

M = dlmread("scores.txt", ";")
delete("scores.txt");

Expected output:

M =
     1     2     3
     4     5     6

Using tab characters as the delimiter

fid = fopen("tabs.txt", "w");
fprintf(fid, "10\t11\t12\n13\t14\t15\n");
fclose(fid);

M = dlmread("tabs.txt", "\t")
delete("tabs.txt");

Expected output:

M =
    10    11    12
    13    14    15

Skipping a header row and column (zero-based offsets)

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

M = dlmread("with_header.txt", ",", 1, 1)
delete("with_header.txt");

Expected output:

M =
     1     2
     3     4

Extracting a rectangular range

fid = fopen("block.txt", "w");
fprintf(fid, "10,11,12,13\n14,15,16,17\n18,19,20,21\n");
fclose(fid);

sub = dlmread("block.txt", ",", [1 1 2 3])
delete("block.txt");

Expected output:

sub =
    15    16    17
    19    20    21

Treating empty fields as zeros

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

M = dlmread("blanks.txt")
delete("blanks.txt");

Expected output:

M =
     1     0     3
     0     5     0
     7     8     0

Reading data with a numeric delimiter code

fid = fopen("pipe.txt", "w");
fprintf(fid, "5|6|7\n8|9|10\n");
fclose(fid);

M = dlmread("pipe.txt", double('|'))
delete("pipe.txt");

Expected output:

M =
     5     6     7
     8     9    10

Using dlmread with coding agents

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

FAQ

Related Io functions

Open-source implementation

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

• View the source for dlmread 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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