# Indexing problem

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## Indexing problem

 Hi,I'm an R user trying to learn Julia. I got hold of some code from the Knet package that I was playing around with. My goal is to set values to zero in a loop based on a logical expression, but I cannot figure out how the indexing works. Any help would be appreciated (the problem lies in w[1,(w[1].-(z))] = 0):using Knetpredict(w,x) = w[1]*x .+ w[2]lambda = 2z = Array{Float64}(1,13)loss(w,x,y) = sumabs2(y - predict(w,x)) / size(y,2)lossgradient = grad(loss)function train(w, data; lr=.1)    for (x,y) in data        dw = lossgradient(w, x, y)        z[:] = lr * lambda        w[1] -= lr * dw[1]        w[2] -= lr * dw[2]        w[1,(w[1].-(z))] = 0    end    return wendurl = "https://archive.ics.uci.edu/ml/machine-learning-databases/housing/housing.data"rawdata = readdlm(download(url))x = rawdata[:,1:13]'x = (x .- mean(x,2)) ./ std(x,2)y = rawdata[:,14:14]'w = Any[ 0.1*randn(1,13), 0 ]niter = 25lossest = zeros(niter)for i=1:niter; train(w, [(x,y)]); lossest[i]=loss(w,x,y); endBest regards,Patrik
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## Re: Indexing problem

 good things to know about how indexing worksThe indices for a Vector, or a column or row of a Matrix start at 1```length(avector)   # gets the number of elements in avectoravector[1]        # gets the first item in avectoravector[end]      # gets the final item in avector avector[1:end]    # gets all elements of avectorint_column_vector = [10, 20, 30] 10 20 30int_column_vector[1] 10# do not use zero as an indexint_column_vector[ 0 ]ERROR: BoundsError:# do not use false, true as indices because avec[ false ] means avec[ 0 ]```in ` w[1,(w[1].-(z))] = 0 `, the second index can simplify to `false`   (consider this)```avec = [ 10, 20, 30 ]avec1 = avec[ 1 ] avec1 == avec[ 1 + false ]avec2 = avec[  2 ]avec2 == avec[ 1 + true ] ```As a start, recheck indexing expressions, be more sure they do what you want them to do.On Wednesday, November 16, 2016 at 1:36:57 PM UTC-5, Patrik Waldmann wrote:Hi,I'm an R user trying to learn Julia. I got hold of some code from the Knet package that I was playing around with. My goal is to set values to zero in a loop based on a logical expression, but I cannot figure out how the indexing works. Any help would be appreciated (the problem lies in w[1,(w[1].-(z))] = 0):using Knetpredict(w,x) = w[1]*x .+ w[2]lambda = 2z = Array{Float64}(1,13)loss(w,x,y) = sumabs2(y - predict(w,x)) / size(y,2)lossgradient = grad(loss)function train(w, data; lr=.1)    for (x,y) in data        dw = lossgradient(w, x, y)        z[:] = lr * lambda        w[1] -= lr * dw[1]        w[2] -= lr * dw[2]        w[1,(w[1].-(z))] = 0    end    return wendurl = "https://archive.ics.uci.edu/ml/machine-learning-databases/housing/housing.data"rawdata = readdlm(download(url))x = rawdata[:,1:13]'x = (x .- mean(x,2)) ./ std(x,2)y = rawdata[:,14:14]'w = Any[ 0.1*randn(1,13), 0 ]niter = 25lossest = zeros(niter)for i=1:niter; train(w, [(x,y)]); lossest[i]=loss(w,x,y); endBest regards,Patrik
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## Re: Indexing problem

 I guess I should have explained my problem clearer. If I run the code without w[1,(w[1].-(z))] = 0, and do:dump(w)Array{Any}((2,))  1: Array{Float64}((1,13)) [-0.681392 0.595298 … 0.893845 -3.5044]  2: Float64 22.447679788630705and println(w[1])[-0.681392 0.595298 -0.394906 0.776983 -1.11178 3.11679 -0.0984956 -2.18501 0.928204 -0.484802 -1.86844 0.893845 -3.5044]println(w[1,1])[-0.681392 0.595298 -0.394906 0.776983 -1.11178 3.11679 -0.0984956 -2.18501 0.928204 -0.484802 -1.86844 0.893845 -3.5044]println(w[1,:])Any[[-0.681392 0.595298 -0.394906 0.776983 -1.11178 3.11679 -0.0984956 -2.18501 0.928204 -0.484802 -1.86844 0.893845 -3.5044]]This is very confusing for an R user like me. How do I access the column indexes of w[1] and apply the logical expression w[1,(w[1].-(z))] = 0 ?PatrikOn Thursday, November 17, 2016 at 6:58:14 AM UTC+1, Jeffrey Sarnoff wrote:good things to know about how indexing worksThe indices for a Vector, or a column or row of a Matrix start at 1```length(avector)   # gets the number of elements in avectoravector[1]        # gets the first item in avectoravector[end]      # gets the final item in avector avector[1:end]    # gets all elements of avectorint_column_vector = [10, 20, 30] 10 20 30int_column_vector[1] 10# do not use zero as an indexint_column_vector[ 0 ]ERROR: BoundsError:# do not use false, true as indices because avec[ false ] means avec[ 0 ]```in ` w[1,(w[1].-(z))] = 0 `, the second index can simplify to `false`   (consider this)```avec = [ 10, 20, 30 ]avec1 = avec[ 1 ] avec1 == avec[ 1 + false ]avec2 = avec[  2 ]avec2 == avec[ 1 + true ] ```As a start, recheck indexing expressions, be more sure they do what you want them to do.On Wednesday, November 16, 2016 at 1:36:57 PM UTC-5, Patrik Waldmann wrote:Hi,I'm an R user trying to learn Julia. I got hold of some code from the Knet package that I was playing around with. My goal is to set values to zero in a loop based on a logical expression, but I cannot figure out how the indexing works. Any help would be appreciated (the problem lies in w[1,(w[1].-(z))] = 0):using Knetpredict(w,x) = w[1]*x .+ w[2]lambda = 2z = Array{Float64}(1,13)loss(w,x,y) = sumabs2(y - predict(w,x)) / size(y,2)lossgradient = grad(loss)function train(w, data; lr=.1)    for (x,y) in data        dw = lossgradient(w, x, y)        z[:] = lr * lambda        w[1] -= lr * dw[1]        w[2] -= lr * dw[2]        w[1,(w[1].-(z))] = 0    end    return wendurl = "https://archive.ics.uci.edu/ml/machine-learning-databases/housing/housing.data"rawdata = readdlm(download(url))x = rawdata[:,1:13]'x = (x .- mean(x,2)) ./ std(x,2)y = rawdata[:,14:14]'w = Any[ 0.1*randn(1,13), 0 ]niter = 25lossest = zeros(niter)for i=1:niter; train(w, [(x,y)]); lossest[i]=loss(w,x,y); endBest regards,Patrik