Chapter 7
Even in quantitative sciences, we
often encounter letters and/or
words that must be processed by
code
You may want to write code that:
• Reads data files that contain both
numbers and words
• Writes data to files (filenames are strings)
• Read a list of files
• Combine a string and a number
• Label plot titles or axes with nums and words
• Prints messages with words and numbers
mixed
Advanced National Seismic System (ANSS)
• http://www.ncedc.org/anss/
• Near real-time data for all global
earthquake events!
• Not just numbers
USGS Current Water Data
• http://waterdata.usgs.gov/nwis/rt
• Near real-time data for streams in
all 50 states!
• Not just numbers
• Recall that
strings are arrays
of characters
• i.e. a matrix of
characters
• Strings can form
rectangular matrices
too!
• Must follow same
matrix rules
• Rows and Cols must
be consistent
• Strings can form
rectangular
matrices too!
• Must follow
same matrix
rules
• Rows and Cols
must be
consistent
• Can “pad” each
row with blank
spaces to make
columns
consistent
• You can read
about “strcat”,
“srtvcat”, and
“char”
What if you want to combine a numeric result with a word?
• fprintf: only prints to the command window (can’t store/use the result)
• sprintf: works just like fprintf, but makes a string
What if you want to label a plot with numbers from data?
• Most MATLAB commands for labeling only accept strings
• Use sprintf to make a string with text+number. Then use the string
What if you want to label a plot with numbers from data?
• Most MATLAB commands for labeling only accept strings
• Use sprintf to make a string with text+number. Then use the string
• Attaway also covers
• deblank
• char
• strtrim
• upper
• lower
• These may come in handy someday
• You can read about these functions for their usage
What if you want to see if two
strings are identical?
• Do not use “==“
• Compares ASCII values
• May work, but is bad
programming style, and can
produce unwanted results
• Use “strcmp” or “strncmp”
• Compares strings
What if you want to see if two
strings are identical?
strcmp
• compares two strings
• returns logical true if identical
strncmp
• compares the first n characters
of two strings
• Returns logical true if identical
• You can read about “strfind”,
“findstr”, “strrep”, and “strtok”.
Now that you know about
various variable types in
MATLAB…
• May want to test whether
a variable contains a
certain type of data
• Various “is” functions do
this
• ischar
• isletter
• isspace
http://www.mathworks.com/help/matlab/ref/is.html
int2str
• Converts an int to a string
• Automatically rounds off if needed
num2str
• Converts an number (double or
int) to a string
• Can specify precision
• If precision not specified, uses
current MATLAB defaults
str2num
• Converts a string to a number
(double)
What if you have a bunch
of files that you want to
load?
• Don’t load each one, one
by one by hand
• Waste of time!
• Knowledge of string
processing can help!
• Use “ls” as a function
• Store result as character
array
Fair Warning:
• Data files are read in the
order that ls reports.
• If not in order, you will
have to sort the data.