Re: read CSV
- To: mathgroup at smc.vnet.net
- Subject: [mg117790] Re: read CSV
- From: David Bailey <dave at removedbailey.co.uk>
- Date: Thu, 31 Mar 2011 04:03:57 -0500 (EST)
- References: <imus7l$i3t$1@smc.vnet.net>
On 30/03/2011 10:13, Alan wrote:
> I've received some files formatted like below.
> How can I read selected columns into a list?
> I'm coming from a background where I'd read in each line,
> discarding the first, then (in this case at least)
> split on the comma, and coerce the type. So I'm happy
> to do that if I can figure out how. (Naturally I could
> preprocess the data into a form that say ReadList
> likes better, but I'm looking for a pure Mathematica solution.)
>
> Thanks,
> Alan Isaac
>
> "x","y","color","pen down?"
> "0","0.26161459854014585","105","true"
> "1","0.2665251497682828","105","true"
> "2","0.29244385081680907","105","true"
> "3","0.31995416628471895","105","true"
>
Here is the code you need. Since you are new to Mathematica, I'll
explain a bit.
1) The Import command will read data from files using the filename
suffix to decide the format it expects. Under Windows, a full pathname
uses backslash characters, which need to be doubled in strings.
2) The data is read in as a 2D array, which can be thought of as a
list of rows - you need to drop one row.
3) Assuming you want the string "true" to become a Mathematica
boolean, you need the /. operator to perform the swap, as shown
In[2]:= data = Import["c:\\ttt\\test.csv"]
Out[2]= {{"x", "y", "color", "pen down?"}, {0, 0.261615, 105,
"true"}, {1, 0.266525, 105, "true"}, {2, 0.292444, 105, "true"}, {3,
0.319954, 105, "true"}}
In[5]:= data =
Drop[data, 1] /. "true" -> True
Out[5]= {{2, 0.292444, 105, True}, {3, 0.319954, 105, True}}
David Bailey
http://www.dbaileyconsultancy.co.uk