Re: [R] computing on expressions
The following seems to work too: expr2 - expression(a0) expr2 - as.expression( bquote(.(expr2[[1]]) b0 ) ) Here as.expression converts the 'call' type returned by bquote to 'expression' type. Thanks again Dunkan. Vadim -Original Message- From: Duncan Murdoch [mailto:murd...@stats.uwo.ca] Sent: Friday, October 03, 2008 11:41 AM To: Vadim Organovich Cc: r-help@r-project.org Subject: Re: [R] computing on expressions On 10/3/2008 11:48 AM, Vadim Organovich wrote: Dear R-users, Suppose I have an expression: expr = expression(a0) and now I want to modify it to expression(a0 b0). The following doesn't work: expr = expression(expr b0) What would be a good way of doing this? I'd avoid using parse because it doesn't generalize well. Here's a way to do it without that. But first, some background: expression() returns a special kind of list that contains language objects. So expr[[1]] is initially a0, and you want to change it to a0 b0. I think you don't really want expr b0, because that would beexpression(a0) b0 which is nonsense. The bquote() function is probably the easiest way to make substitutions. The idea is that you write out the answer you want within bquote(), using .() around things you want substituted. (You can also use the substitute() function, but it's a little trickier.) Putting these together, this gives you the final result you want: expr - expression(a0) expr[[1]] - bquote( .(expr[[1]]) b0 ) The following lines almost give you what you want: expr2 - expression(a0) expr2 - bquote( expression( .(expr2[[1]]) b0 ) ) but not quite: expr2 becomes an unevaluated call to the expression() function, not an actual expression (though they print the same). You need this for the equivalent to the first version: expr2 - expression(a0) expr2 - eval( bquote( expression( .(expr2[[1]]) b0 ) ) ) Duncan Murdoch Note: This email is for the confidential use of the named addressee(s) only and may contain proprietary, confidential or privileged information. If you are not the intended recipient, you are hereby notified that any review, dissemination or copying of this email is strictly prohibited, and to please notify the sender immediately and destroy this email and any attachments. Email transmission cannot be guaranteed to be secure or error-free. Jump Trading, therefore, does not make any guarantees as to the completeness or accuracy of this email or any attachments. This email is for informational purposes only and does not constitute a recommendation, offer, request or solicitation of any kind to buy, sell, subscribe, redeem or perform any type of transaction of a financial product. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] computing on expressions
Try this: parse(text = paste(capture.output(expr[[1]]), b 0)) On Fri, Oct 3, 2008 at 12:48 PM, Vadim Organovich [EMAIL PROTECTED] wrote: Dear R-users, Suppose I have an expression: expr = expression(a0) and now I want to modify it to expression(a0 b0). The following doesn't work: expr = expression(expr b0) What would be a good way of doing this? Thanks, Vadim Note: This email is for the confidential use of the named addressee(s) only and may contain proprietary, confidential or privileged information. If you are not the intended recipient, you are hereby notified that any review, dissemination or copying of this email is strictly prohibited, and to please notify the sender immediately and destroy this email and any attachments. Email transmission cannot be guaranteed to be secure or error-free. Jump Trading, therefore, does not make any guarantees as to the completeness or accuracy of this email or any attachments. This email is for informational purposes only and does not constitute a recommendation, offer, request or solicitation of any kind to buy, sell, subscribe, redeem or perform any type of transaction of a financial product. [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. -- Henrique Dallazuanna Curitiba-Paraná-Brasil 25° 25' 40 S 49° 16' 22 O __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] computing on expressions
Thanks! Here is a less verbose variation based on suggestion by Phil Spector: parse(text=paste(expression(a0), b0)) From: Henrique Dallazuanna [EMAIL PROTECTED] Sent: Friday, October 03, 2008 11:08 AM To: Vadim Organovich Cc: r-help@r-project.org Subject: Re: [R] computing on expressions Try this: parse(text = paste(capture.output(expr[[1]]), b 0)) On Fri, Oct 3, 2008 at 12:48 PM, Vadim Organovich [EMAIL PROTECTED] wrote: Dear R-users, Suppose I have an expression: expr = expression(a0) and now I want to modify it to expression(a0 b0). The following doesn't work: expr = expression(expr b0) What would be a good way of doing this? Thanks, Vadim Note: This email is for the confidential use of the named addressee(s) only and may contain proprietary, confidential or privileged information. If you are not the intended recipient, you are hereby notified that any review, dissemination or copying of this email is strictly prohibited, and to please notify the sender immediately and destroy this email and any attachments. Email transmission cannot be guaranteed to be secure or error-free. Jump Trading, therefore, does not make any guarantees as to the completeness or accuracy of this email or any attachments. This email is for informational purposes only and does not constitute a recommendation, offer, request or solicitation of any kind to buy, sell, subscribe, redeem or perform any type of transaction of a financial product. [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. -- Henrique Dallazuanna Curitiba-Paraná-Brasil 25° 25' 40 S 49° 16' 22 O Note: This email is for the confidential use of the named addressee(s) only and may contain proprietary, confidential or privileged information. If you are not the intended recipient, you are hereby notified that any review, dissemination or copying of this email is strictly prohibited, and to please notify the sender immediately and destroy this email and any attachments. Email transmission cannot be guaranteed to be secure or error-free. Jump Trading, therefore, does not make any guarantees as to the completeness or accuracy of this email or any attachments. This email is for informational purposes only and does not constitute a recommendation, offer, request or solicitation of any kind to buy, sell, subscribe, redeem or perform any type of transaction of a financial product. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
