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Re: ReadList

  • To: mathgroup at
  • Subject: [mg18855] Re: [mg18787] ReadList
  • From: "Tomas Garza" <tgarza at>
  • Date: Thu, 22 Jul 1999 22:57:50 -0400
  • Sender: owner-wri-mathgroup at

James l. Fisher [jlfisher at] wrote:

> I want to read the following data which is in ascii form into a list
> 09/22/98 12:15 2.36
> 09/22/98 12:30 2.37
> 09/22/98 12:45 2.38
> etc
>  How can I use ReadList, or some other command, to enter this
> into the form
>  {{09/22/98,12:15,2.36},{09/22/98,12:30,2.37},{09/22/98,12:45, 2.38}}
> How could I read each column into a seperate list also.


I assume your data are, e.g., in an Excel table. First, save them as
tab-delimited text in a file origdata.txt, say. Then you can read them in

data = ReadList["origdata.txt", Word, RecordLists -> True]
{{"09/22/98", "12:15", "2.36"}, {"09/22/98", "12:30", "2.37"}, {"09/22/98",
    "12:45", "2.38"}}

You can place each column in a separate list with

fil1 = Transpose[data][[1]]
{"09/22/98", "09/22/98", "09/22/98"}
fil2 = Transpose[data][[2]]
{"12:15", "12:30", "12:45"}
fil3 = Transpose[data][[3]]
{"2.36", "2.37", "2.38"}

The thing is, all the values in data are strings. If you want to do
something useful with them, they have to be converted to numbers. But in
their present form only the third column can be converted directly:

newdata = data /. {x1_, x2_, x3_String} :> {x1, x2, ToExpression[x3]}
{{"09/22/98", "12:15", 2.36}, {"09/22/98", "12:30", 2.37}, {"09/22/98",
    "12:45", 2.38}}

If you want to use the first two columns, e.g. for plotting or regression
analysis, you must express their elements in numerical form. You may take an
arbitrary origin for date, so that each date is referred to it, and the same
for the time of day. So, e.g., let 09/20/98 be the origin for date, and 0:00
the origin for time of day. Your data can then be prepared in Excel, which
has a good menu for time and date functions, or you can use functions Date
and FromDate in Mathematica. The idea is that all your date and time values
be expressed as numbers.

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