Page 29 - MATLAB Recipes for Earth Sciences

20 2 Introduction to MATLAB

ries, most data arrive as ASCII files. Consider a simple data set stored in a
table such as
SampleID Percent C Percent S
101 0.3657 0.0636
102 0.2208 0.1135
103 0.5353 0.5191
104 0.5009 0.5216
105 0.5415 -999
106 0.501 -999

The first row contains the variable names. The columns provide the data for
each sample. The absurd value -999 marks missing data in the data set. Two
things have to be changed in order to convert this table into MATLAB format.
First, MATLAB uses NaN as the arithmetic representation for Not-a-Number

that can be used to mark gaps. Second, you should comment the first line by
typing a percent sign, %, at the beginning of the line.
%SampleID Percent C Percent S
101 0.3657 0.0636
102 0.2208 0.1135
103 0.5353 0.5191
104 0.5009 0.5216
105 0.5415 NaN
106 0.501 NaN

MATLAB ignores any text appearing after the percent sign and continues
processing on the next line. After editing this table in a text editor, such as
the MATLAB Editor, it is saved as ASCII text fi le geochem.txt in the current
working directory (Fig. 2.2). MATLAB now imports the data from this fi le
with the load command:

load geochem.txt

MATLAB loads the contents of file and assigns the matrix to a variable
named after the fi lename geochem. Typing
whos

yields
Name Size Bytes Class
geochem 6x3 144 double array
Grand total is 18 elements using 144 bytes
The command save now allows to store workspace variables in a binary
format.
save geochem_new.mat