data

The Data Editor is accessible via the APPS menu.

Choose Current to revisit your last data file, Open to open an old data file, or New to create a new data file.

You can also open the Matrix Editor and the List Editor from the same menu.
Variable is the name of the file. The calculator will automatically save the data under this name.
To delete a data file, enter delvar and the name of the file on the command line of the HOME screen, or use the VAR-LINK menu.
You need to hit ENTER twice to exit this screen.

You can use a formula to fill the entries in a column by highlighting the column heading and typing the formula.
The columns of a data file are lists, so any commands that operate on lists will work on the columns.
(Most commands that work on individual numbers will also work on lists.)
You can also enter numbers or expressions in the cells by hand, or transfer a data variable from another calculator or a computer.

You can define columns in terms of other columns. Highlight the column heading and type in the formula.
If you want to change the formula, highlight the heading, push ENTER, and type in a new formula.
If you want to remove the formula altogether, highlight the heading, push ENTER and then CLEAR.
This does not remove the data in the column, it just removes the formula. Use the Util (F6) menu to delete the contents of a row, a column, or an individual cell.
Nothing stops you from defining c1 = c1+3. If c1 is empty at the time, you get an error message. If c1 has data, each entry is replaced by itself plus 3.
A couple of useful list commands are shift (shift(c1,1) here would produce the list { 2, 3, 4, 5, 6, 7, 8, 9, 10, undef }) and cumsum (cumsum(c1) here would produce the list { 1, 3, 6, 10, 15, 21, 28, 36, 45, 55 }.

The first entry in the second column is called r1c2. The lock symbol at the beginning of the command line indicates that you can't edit the individual cell, since its contents are determined by the formula for the whole column. If you delete the column formula, the cells are unlocked but the entries don't change until you change them.

One useful thing you can do with the data in a data file is plot them on the GRAPH screen.
To start the procedure, push F2 to go to the Plot Setup menu. Then F1 lets you define the plot.

You have a choice of

Plot Type (scatter and xyline plot points with x-coordinates from one column of your data and y-coordinates from another; xyline connects the dots and scatter doesn't.)
Mark (Box, Cross, Plus, and Square look like what you'd expect. Dot does, too, but it's very hard to see.)
For scatter and xyline plots, you specify which column has your x-coordinates and which one has your y-coordinates.

You have to hit ENTER more than once to exit this menu.

The check mark says the plot will be graphed. (You can change that with F4.)
The picture indicates a scatter plot.
The square shows how the points will be marked.
The rest of the line says that x-coordinates come from c1 and y-coordinates from c2.

This is what you see if you go to the GRAPH screen. ZoomData adjusts the screen to show all the data points.
(You also end up with this screen if you choose ZoomData from the Zoom menu on either the Y= screen or the WINDOW screen.)

You can get back to the Data/Matrix editor via the APPS menu or by pushing 2nd APPS.
From there, the Calc (F5) menu gets you to the Calculate screen.

From the Calculate screen you can calculate

one-variable statistics (maximum, mean, sum of squares, standard deviation, etc.) on any one of your data columns,
two-variable statistics (one-variable for each of two variables, plus sum of products) on any two of your data columns,
regression curves of various sorts for any two of your data columns. (This attempts to find the curve with a specified type of formula which comes closest to passing through the points with x- and y-coordinates given by two of your data columns.)

If you choose Linear Regression, you're looking for the formula for the straight line that comes closest to passing through all the points plotted earlier.

a and b give the formula for the line. corr and R² measure how well the curve fits the data (closer to 1 is better).

Making the choice Store RegEQ to y1(x) on the Calculate screen means that when we go back to the GRAPH screen we see not only the data points but the line that's supposed to fit them best.

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